Postfix manual - smtpd(8)

    SMTPD(8)                                                              SMTPD(8)

    NAME
           smtpd - Postfix SMTP server

    SYNOPSIS
           smtpd [generic Postfix daemon options]

           sendmail -bs

    DESCRIPTION
           The  SMTP  server  accepts network connection requests and
           performs zero or more SMTP  transactions  per  connection.
           Each received message is piped through the cleanup(8) dae-
           mon, and is placed into the incoming queue as  one  single
           queue  file.   For  this  mode  of  operation, the program
           expects to be run from the master(8) process manager.

           Alternatively, the SMTP server be can run  in  stand-alone
           mode;  this is traditionally obtained with "sendmail -bs".
           When the SMTP server runs stand-alone with non $mail_owner
           privileges, it receives mail even while the mail system is
           not running, deposits messages directly into the  maildrop
           queue,  and disables the SMTP server's access policies. As
           of Postfix version 2.3, the SMTP server refuses to receive
           mail  from  the  network when it runs with non $mail_owner
           privileges.

           The SMTP server implements a variety of policies for  con-
           nection  requests, and for parameters given to HELO, ETRN,
           MAIL FROM, VRFY and RCPT TO commands.  They  are  detailed
           below and in the main.cf configuration file.

    SECURITY
           The SMTP server is moderately security-sensitive. It talks
           to SMTP clients and to DNS servers  on  the  network.  The
           SMTP server can be run chrooted at fixed low privilege.

    STANDARDS
           RFC 821 (SMTP protocol)
           RFC 1123 (Host requirements)
           RFC 1652 (8bit-MIME transport)
           RFC 1869 (SMTP service extensions)
           RFC 1870 (Message Size Declaration)
           RFC 1985 (ETRN command)
           RFC 2034 (SMTP Enhanced Error Codes)
           RFC 2554 (AUTH command)
           RFC 2821 (SMTP protocol)
           RFC 2920 (SMTP Pipelining)
           RFC 3207 (STARTTLS command)
           RFC 3461 (SMTP DSN Extension)
           RFC 3463 (Enhanced Status Codes)
           RFC 3848 (ESMTP Transmission Types)
           RFC 4954 (AUTH command)

    DIAGNOSTICS
           Problems and transactions are logged to syslogd(8).

           Depending  on the setting of the notify_classes parameter,
           the postmaster is notified of bounces, protocol  problems,
           policy violations, and of other trouble.

    CONFIGURATION PARAMETERS
           Changes   to  main.cf  are  picked  up  automatically,  as
           smtpd(8) processes run for only a limited amount of  time.
           Use the command "postfix reload" to speed up a change.

           The  text  below  provides  only  a parameter summary. See
           postconf(5) for more details including examples.

    COMPATIBILITY CONTROLS
           The following parameters work around implementation errors
           in  other software, and/or allow you to override standards
           in order to prevent undesirable use.

           broken_sasl_auth_clients (no)
                  Enable inter-operability  with  SMTP  clients  that
                  implement  an  obsolete version of the AUTH command
                  (RFC 4954).

           disable_vrfy_command (no)
                  Disable the SMTP VRFY command.

           smtpd_noop_commands (empty)
                  List of  commands  that  the  Postfix  SMTP  server
                  replies  to with "250 Ok", without doing any syntax
                  checks and without changing state.

           strict_rfc821_envelopes (no)
                  Require that addresses received in SMTP  MAIL  FROM
                  and RCPT TO commands are enclosed with <>, and that
                  those addresses do not contain RFC 822  style  com-
                  ments or phrases.

           Available in Postfix version 2.1 and later:

           resolve_null_domain (no)
                  Resolve an address that ends in the "@" null domain
                  as if the local hostname were specified, instead of
                  rejecting the address as invalid.

           smtpd_reject_unlisted_sender (no)
                  Request  that  the Postfix SMTP server rejects mail
                  from  unknown  sender  addresses,  even   when   no
                  explicit  reject_unlisted_sender access restriction
                  is specified.

           smtpd_sasl_exceptions_networks (empty)
                  What remote SMTP clients the  Postfix  SMTP  server
                  will not offer AUTH support to.

           Available in Postfix version 2.2 and later:

           smtpd_discard_ehlo_keyword_address_maps (empty)
                  Lookup  tables,  indexed  by the remote SMTP client
                  address, with case insensitive lists of  EHLO  key-
                  words  (pipelining,  starttls, auth, etc.) that the
                  SMTP server will not send in the EHLO response to a
                  remote SMTP client.

           smtpd_discard_ehlo_keywords (empty)
                  A  case insensitive list of EHLO keywords (pipelin-
                  ing, starttls, auth, etc.)  that  the  SMTP  server
                  will not send in the EHLO response to a remote SMTP
                  client.

           smtpd_delay_open_until_valid_rcpt (yes)
                  Postpone the start  of  an  SMTP  mail  transaction
                  until a valid RCPT TO command is received.

           Available in Postfix version 2.3 and later:

           smtpd_tls_always_issue_session_ids (yes)
                  Force  the  Postfix SMTP server to issue a TLS ses-
                  sion id, even when TLS session  caching  is  turned
                  off (smtpd_tls_session_cache_database is empty).

    ADDRESS REWRITING CONTROLS
           See  the  ADDRESS_REWRITING_README document for a detailed
           discussion of Postfix address rewriting.

           receive_override_options (empty)
                  Enable or disable  recipient  validation,  built-in
                  content filtering, or address mapping.

           Available in Postfix version 2.2 and later:

           local_header_rewrite_clients (permit_inet_interfaces)
                  Rewrite message header addresses in mail from these
                  clients and update incomplete  addresses  with  the
                  domain name in $myorigin or $mydomain; either don't
                  rewrite message headers from other clients at  all,
                  or  rewrite  message  headers and update incomplete
                  addresses  with  the  domain   specified   in   the
                  remote_header_rewrite_domain parameter.

    AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS
           As  of  version 1.0, Postfix can be configured to send new
           mail to an external  content  filter  AFTER  the  mail  is
           queued.  This  content  filter  is expected to inject mail
           back into a (Postfix or other) MTA for  further  delivery.
           See the FILTER_README document for details.

           content_filter (empty)
                  The  name of a mail delivery transport that filters
                  mail after it is queued.

    BEFORE QUEUE EXTERNAL CONTENT INSPECTION CONTROLS
           As of version 2.1, the Postfix SMTP server can be  config-
           ured  to send incoming mail to a real-time SMTP-based con-
           tent filter BEFORE mail is queued.  This content filter is
           expected  to  inject  mail  back  into  Postfix.   See the
           SMTPD_PROXY_README document for details on how to  config-
           ure and operate this feature.

           smtpd_proxy_filter (empty)
                  The  hostname  and  TCP  port of the mail filtering
                  proxy server.

           smtpd_proxy_ehlo ($myhostname)
                  How the Postfix SMTP server announces itself to the
                  proxy filter.

           smtpd_proxy_timeout (100s)
                  The time limit for connecting to a proxy filter and
                  for sending or receiving information.

    BEFORE QUEUE MILTER CONTROLS
           As of version 2.3, Postfix supports the Sendmail version 8
           Milter  (mail  filter) protocol. These content filters run
           outside Postfix. They can inspect the SMTP command  stream
           and  the  message  content,  and can request modifications
           before mail is queued. For details see  the  MILTER_README
           document.

           smtpd_milters (empty)
                  A list of Milter (mail filter) applications for new
                  mail that arrives via the Postfix smtpd(8)  server.

           milter_protocol (2)
                  The  mail filter protocol version and optional pro-
                  tocol extensions for communication  with  a  Milter
                  (mail filter) application.

           milter_default_action (tempfail)
                  The  default  action  when  a  Milter (mail filter)
                  application is unavailable or mis-configured.

           milter_macro_daemon_name ($myhostname)
                  The {daemon_name} macro value for Milter (mail fil-
                  ter) applications.

           milter_macro_v ($mail_name $mail_version)
                  The {v} macro value for Milter (mail filter) appli-
                  cations.

           milter_connect_timeout (30s)
                  The time limit for connecting  to  a  Milter  (mail
                  filter)  application,  and for negotiating protocol
                  options.

           milter_command_timeout (30s)
                  The time limit for sending an  SMTP  command  to  a
                  Milter (mail filter) application, and for receiving
                  the response.

           milter_content_timeout (300s)
                  The time limit for sending  message  content  to  a
                  Milter (mail filter) application, and for receiving
                  the response.

           milter_connect_macros (see postconf -n output)
                  The macros that are sent to  Milter  (mail  filter)
                  applications  after  completion  of an SMTP connec-
                  tion.

           milter_helo_macros (see postconf -n output)
                  The macros that are sent to  Milter  (mail  filter)
                  applications after the SMTP HELO or EHLO command.

           milter_mail_macros (see postconf -n output)
                  The  macros  that  are sent to Milter (mail filter)
                  applications after the SMTP MAIL FROM command.

           milter_rcpt_macros (see postconf -n output)
                  The macros that are sent to  Milter  (mail  filter)
                  applications after the SMTP RCPT TO command.

           milter_data_macros (see postconf -n output)
                  The  macros  that  are  sent to version 4 or higher
                  Milter (mail filter) applications  after  the  SMTP
                  DATA command.

           milter_unknown_command_macros (see postconf -n output)
                  The  macros  that  are  sent to version 3 or higher
                  Milter (mail filter) applications after an  unknown
                  SMTP command.

           milter_end_of_header_macros (see postconf -n output)
                  The  macros  that  are sent to Milter (mail filter)
                  applications after the end of the message header.

           milter_end_of_data_macros (see postconf -n output)
                  The macros that are sent to  Milter  (mail  filter)
                  applications after the message end-of-data.

    GENERAL CONTENT INSPECTION CONTROLS
           The  following parameters are applicable for both built-in
           and external content filters.

           Available in Postfix version 2.1 and later:

           receive_override_options (empty)
                  Enable or disable  recipient  validation,  built-in
                  content filtering, or address mapping.

    EXTERNAL CONTENT INSPECTION CONTROLS
           The  following  parameters are applicable for both before-
           queue and after-queue content filtering.

           Available in Postfix version 2.1 and later:

           smtpd_authorized_xforward_hosts (empty)
                  What SMTP clients are allowed to use  the  XFORWARD
                  feature.

    SASL AUTHENTICATION CONTROLS
           Postfix  SASL  support (RFC 4954) can be used to authenti-
           cate remote SMTP clients to the Postfix SMTP  server,  and
           to  authenticate  the Postfix SMTP client to a remote SMTP
           server.  See the SASL_README document for details.

           broken_sasl_auth_clients (no)
                  Enable inter-operability  with  SMTP  clients  that
                  implement  an  obsolete version of the AUTH command
                  (RFC 4954).

           smtpd_sasl_auth_enable (no)
                  Enable SASL  authentication  in  the  Postfix  SMTP
                  server.

           smtpd_sasl_local_domain (empty)
                  The  name  of  the Postfix SMTP server's local SASL
                  authentication realm.

           smtpd_sasl_security_options (noanonymous)
                  Postfix SMTP server SASL security  options;  as  of
                  Postfix  2.3 the list of available features depends
                  on the SASL server implementation that is  selected
                  with smtpd_sasl_type.

           smtpd_sender_login_maps (empty)
                  Optional  lookup  table  with  the SASL login names
                  that own sender (MAIL FROM) addresses.

           Available in Postfix version 2.1 and later:

           smtpd_sasl_exceptions_networks (empty)
                  What remote SMTP clients the  Postfix  SMTP  server
                  will not offer AUTH support to.

           Available in Postfix version 2.1 and 2.2:

           smtpd_sasl_application_name (smtpd)
                  The  application  name that the Postfix SMTP server
                  uses for SASL server initialization.

           Available in Postfix version 2.3 and later:

           smtpd_sasl_authenticated_header (no)
                  Report the SASL  authenticated  user  name  in  the
                  smtpd(8) Received message header.

           smtpd_sasl_path (smtpd)
                  Implementation-specific  information that the Post-
                  fix SMTP server passes through to the SASL  plug-in
                  implementation     that     is     selected    with
                  smtpd_sasl_type.

           smtpd_sasl_type (cyrus)
                  The SASL plug-in type that the Postfix SMTP  server
                  should use for authentication.

           Available in Postfix version 2.5 and later:

           cyrus_sasl_config_path (empty)
                  Search  path  for Cyrus SASL application configura-
                  tion files,  currently  used  only  to  locate  the
                  $smtpd_sasl_path.conf file.

    STARTTLS SUPPORT CONTROLS
           Detailed  information  about STARTTLS configuration may be
           found in the TLS_README document.

           smtpd_tls_security_level (empty)
                  The SMTP TLS security level for  the  Postfix  SMTP
                  server;  when  a non-empty value is specified, this
                  overrides the obsolete parameters smtpd_use_tls and
                  smtpd_enforce_tls.

           smtpd_sasl_tls_security_options         ($smtpd_sasl_secu-
           rity_options)
                  The  SASL  authentication security options that the
                  Postfix SMTP server uses  for  TLS  encrypted  SMTP
                  sessions.

           smtpd_starttls_timeout (300s)
                  The  time  limit  for Postfix SMTP server write and
                  read operations during  TLS  startup  and  shutdown
                  handshake procedures.

           smtpd_tls_CAfile (empty)
                  The  file with the certificate of the certification
                  authority (CA) that issued the Postfix SMTP  server
                  certificate.

           smtpd_tls_CAfile (empty)
                  The  file with the certificate of the certification
                  authority (CA) that issued the Postfix SMTP  server
                  certificate.

           smtpd_tls_always_issue_session_ids (yes)
                  Force  the  Postfix SMTP server to issue a TLS ses-
                  sion id, even when TLS session  caching  is  turned
                  off (smtpd_tls_session_cache_database is empty).

           smtpd_tls_ask_ccert (no)
                  Ask  a remote SMTP client for a client certificate.

           smtpd_tls_auth_only (no)
                  When TLS encryption is optional in the Postfix SMTP
                  server,  do not announce or accept SASL authentica-
                  tion over unencrypted connections.

           smtpd_tls_ccert_verifydepth (9)
                  The verification depth for remote SMTP client  cer-
                  tificates.

           smtpd_tls_cert_file (empty)
                  File  with  the Postfix SMTP server RSA certificate
                  in PEM format.

           smtpd_tls_exclude_ciphers (empty)
                  List of ciphers or cipher types to exclude from the
                  SMTP server cipher list at all TLS security levels.

           smtpd_tls_dcert_file (empty)
                  File with the Postfix SMTP server  DSA  certificate
                  in PEM format.

           smtpd_tls_dh1024_param_file (empty)
                  File  with  DH  parameters  that  the  Postfix SMTP
                  server should use with EDH ciphers.

           smtpd_tls_dh512_param_file (empty)
                  File with  DH  parameters  that  the  Postfix  SMTP
                  server should use with EDH ciphers.

           smtpd_tls_dkey_file ($smtpd_tls_dcert_file)
                  File  with  the Postfix SMTP server DSA private key
                  in PEM format.

           smtpd_tls_key_file ($smtpd_tls_cert_file)
                  File with the Postfix SMTP server RSA  private  key
                  in PEM format.

           smtpd_tls_loglevel (0)
                  Enable  additional  Postfix  SMTP server logging of
                  TLS activity.

           smtpd_tls_mandatory_ciphers (medium)
                  The minimum TLS cipher grade that the Postfix  SMTP
                  server will use with mandatory TLS encryption.

           smtpd_tls_mandatory_exclude_ciphers (empty)
                  Additional  list  of  ciphers  or  cipher  types to
                  exclude from the SMTP server cipher list at  manda-
                  tory TLS security levels.

           smtpd_tls_mandatory_protocols (SSLv3, TLSv1)
                  The  SSL/TLS protocols accepted by the Postfix SMTP
                  server with mandatory TLS encryption.

           smtpd_tls_received_header (no)
                  Request  that  the  Postfix  SMTP  server  produces
                  Received:  message headers that include information
                  about the protocol and cipher used, as well as  the
                  client  CommonName  and  client  certificate issuer
                  CommonName.

           smtpd_tls_req_ccert (no)
                  With mandatory TLS encryption,  require  a  trusted
                  remote  SMTP  client  certificate in order to allow
                  TLS connections to proceed.

           smtpd_tls_session_cache_database (empty)
                  Name of the file containing  the  optional  Postfix
                  SMTP server TLS session cache.

           smtpd_tls_session_cache_timeout (3600s)
                  The expiration time of Postfix SMTP server TLS ses-
                  sion cache information.

           smtpd_tls_wrappermode (no)
                  Run the Postfix SMTP  server  in  the  non-standard
                  "wrapper"  mode, instead of using the STARTTLS com-
                  mand.

           tls_daemon_random_bytes (32)
                  The number of pseudo-random bytes that  an  smtp(8)
                  or  smtpd(8)  process  requests  from the tlsmgr(8)
                  server in order to seed its internal pseudo  random
                  number generator (PRNG).

           tls_high_cipherlist
           (ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
                  The OpenSSL cipherlist for "HIGH" grade ciphers.

           tls_medium_cipherlist (ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
                  The OpenSSL cipherlist for "MEDIUM" or higher grade
                  ciphers.

           tls_low_cipherlist (ALL:!EXPORT:+RC4:@STRENGTH)
                  The OpenSSL cipherlist for "LOW"  or  higher  grade
                  ciphers.

           tls_export_cipherlist (ALL:+RC4:@STRENGTH)
                  The OpenSSL cipherlist for "EXPORT" or higher grade
                  ciphers.

           tls_null_cipherlist (eNULL:!aNULL)
                  The OpenSSL cipherlist  for  "NULL"  grade  ciphers
                  that provide authentication without encryption.

           Available in Postfix version 2.5 and later:

           smtpd_tls_fingerprint_digest (md5)
                  The  message  digest  algorithm  used  to construct
                  client-certificate         fingerprints         for
                  check_ccert_access and permit_tls_clientcerts.

    OBSOLETE STARTTLS CONTROLS
           The  following configuration parameters exist for compati-
           bility with Postfix versions before 2.3. Support for these
           will be removed in a future release.

           smtpd_use_tls (no)
                  Opportunistic  TLS:  announce  STARTTLS  support to
                  SMTP clients, but do not require that  clients  use
                  TLS encryption.

           smtpd_enforce_tls (no)
                  Mandatory  TLS:  announce  STARTTLS support to SMTP
                  clients, and require that clients use  TLS  encryp-
                  tion.

           smtpd_tls_cipherlist (empty)
                  Obsolete Postfix < 2.3 control for the Postfix SMTP
                  server TLS cipher list.

    VERP SUPPORT CONTROLS
           With VERP style delivery,  each  recipient  of  a  message
           receives a customized copy of the message with his/her own
           recipient address encoded in the envelope sender  address.
           The VERP_README file describes configuration and operation
           details of Postfix support for  variable  envelope  return
           path addresses.  VERP style delivery is requested with the
           SMTP XVERP command or with the "sendmail -V"  command-line
           option  and is available in Postfix version 1.1 and later.

           default_verp_delimiters (+=)
                  The two default VERP delimiter characters.

           verp_delimiter_filter (-=+)
                  The characters Postfix accepts  as  VERP  delimiter
                  characters  on the Postfix sendmail(1) command line
                  and in SMTP commands.

           Available in Postfix version 1.1 and 2.0:

           authorized_verp_clients ($mynetworks)
                  What SMTP clients are allowed to specify the  XVERP
                  command.

           Available in Postfix version 2.1 and later:

           smtpd_authorized_verp_clients ($authorized_verp_clients)
                  What  SMTP clients are allowed to specify the XVERP
                  command.

    TROUBLE SHOOTING CONTROLS
           The DEBUG_README document describes how to debug parts  of
           the  Postfix mail system. The methods vary from making the
           software log a lot of detail, to running some daemon  pro-
           cesses under control of a call tracer or debugger.

           debug_peer_level (2)
                  The  increment  in  verbose  logging  level  when a
                  remote client or server matches a  pattern  in  the
                  debug_peer_list parameter.

           debug_peer_list (empty)
                  Optional  list  of remote client or server hostname
                  or network address patterns that cause the  verbose
                  logging  level  to increase by the amount specified
                  in $debug_peer_level.

           error_notice_recipient (postmaster)
                  The recipient  of  postmaster  notifications  about
                  mail  delivery  problems that are caused by policy,
                  resource, software or protocol errors.

           internal_mail_filter_classes (empty)
                  What categories of Postfix-generated mail are  sub-
                  ject   to   before-queue   content   inspection  by
                  non_smtpd_milters, header_checks and body_checks.

           notify_classes (resource, software)
                  The list of error classes that are reported to  the
                  postmaster.

           soft_bounce (no)
                  Safety net to keep mail queued that would otherwise
                  be returned to the sender.

           Available in Postfix version 2.1 and later:

           smtpd_authorized_xclient_hosts (empty)
                  What SMTP clients are allowed to  use  the  XCLIENT
                  feature.

    KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS
           As  of  Postfix  version 2.0, the SMTP server rejects mail
           for unknown recipients. This prevents the mail queue  from
           clogging  up  with  undeliverable  MAILER-DAEMON messages.
           Additional  information  on   this   topic   is   in   the
           LOCAL_RECIPIENT_README and ADDRESS_CLASS_README documents.

           show_user_unknown_table_name (yes)
                  Display the name of  the  recipient  table  in  the
                  "User unknown" responses.

           canonical_maps (empty)
                  Optional  address mapping lookup tables for message
                  headers and envelopes.

           recipient_canonical_maps (empty)
                  Optional address mapping lookup tables for envelope
                  and header recipient addresses.

           Parameters concerning known/unknown local recipients:

           mydestination  ($myhostname,  localhost.$mydomain,  local-
           host)
                  The  list  of  domains  that  are delivered via the
                  $local_transport mail delivery transport.

           inet_interfaces (all)
                  The network interface addresses that this mail sys-
                  tem receives mail on.

           proxy_interfaces (empty)
                  The network interface addresses that this mail sys-
                  tem receives mail on by way of a proxy  or  network
                  address translation unit.

           inet_protocols (ipv4)
                  The  Internet protocols Postfix will attempt to use
                  when making or accepting connections.

           local_recipient_maps             (proxy:unix:passwd.byname
           $alias_maps)
                  Lookup tables with all names or addresses of  local
                  recipients:  a  recipient address is local when its
                  domain matches $mydestination, $inet_interfaces  or
                  $proxy_interfaces.

           unknown_local_recipient_reject_code (550)
                  The  numerical  Postfix  SMTP  server response code
                  when   a   recipient   address   is   local,    and
                  $local_recipient_maps  specifies  a  list of lookup
                  tables that does not match the recipient.

           Parameters concerning known/unknown  recipients  of  relay
           destinations:

           relay_domains ($mydestination)
                  What  destination  domains (and subdomains thereof)
                  this system will relay mail to.

           relay_recipient_maps (empty)
                  Optional lookup tables with all valid addresses  in
                  the domains that match $relay_domains.

           unknown_relay_recipient_reject_code (550)
                  The numerical Postfix SMTP server reply code when a
                  recipient  address  matches   $relay_domains,   and
                  relay_recipient_maps  specifies  a  list  of lookup
                  tables that does not match the recipient address.

           Parameters concerning known/unknown recipients in  virtual
           alias domains:

           virtual_alias_domains ($virtual_alias_maps)
                  Postfix is final destination for the specified list
                  of virtual alias  domains,  that  is,  domains  for
                  which  all  addresses  are  aliased to addresses in
                  other local or remote domains.

           virtual_alias_maps ($virtual_maps)
                  Optional lookup tables  that  alias  specific  mail
                  addresses  or  domains  to  other  local  or remote
                  address.

           unknown_virtual_alias_reject_code (550)
                  The SMTP server reply code when a recipient address
                  matches     $virtual_alias_domains,    and    $vir-
                  tual_alias_maps specifies a list of  lookup  tables
                  that does not match the recipient address.

           Parameters  concerning known/unknown recipients in virtual
           mailbox domains:

           virtual_mailbox_domains ($virtual_mailbox_maps)
                  Postfix is final destination for the specified list
                  of   domains;  mail  is  delivered  via  the  $vir-
                  tual_transport mail delivery transport.

           virtual_mailbox_maps (empty)
                  Optional lookup tables with all valid addresses  in
                  the domains that match $virtual_mailbox_domains.

           unknown_virtual_mailbox_reject_code (550)
                  The SMTP server reply code when a recipient address
                  matches   $virtual_mailbox_domains,    and    $vir-
                  tual_mailbox_maps specifies a list of lookup tables
                  that does not match the recipient address.

    RESOURCE AND RATE CONTROLS
           The following parameters limit resource usage by the  SMTP
           server and/or control client request rates.

           line_length_limit (2048)
                  Upon  input,  long lines are chopped up into pieces
                  of at most this length; upon delivery,  long  lines
                  are reconstructed.

           queue_minfree (0)
                  The  minimal  amount  of free space in bytes in the
                  queue file system that is needed to receive mail.

           message_size_limit (10240000)
                  The maximal size in bytes of a  message,  including
                  envelope information.

           smtpd_recipient_limit (1000)
                  The  maximal  number of recipients that the Postfix
                  SMTP server accepts per message delivery request.

           smtpd_timeout (300s)
                  The time limit for sending a  Postfix  SMTP  server
                  response  and  for  receiving  a remote SMTP client
                  request.

           smtpd_history_flush_threshold (100)
                  The maximal number of lines  in  the  Postfix  SMTP
                  server  command  history  before it is flushed upon
                  receipt of EHLO, RSET, or end of DATA.

           Available in Postfix version 2.3 and later:

           smtpd_peername_lookup (yes)
                  Attempt to look up the remote SMTP client hostname,
                  and  verify  that  the  name  matches the client IP
                  address.

           The per SMTP client connection count and request rate lim-
           its are implemented in co-operation with the anvil(8) ser-
           vice, and are available in Postfix version 2.2 and  later.

           smtpd_client_connection_count_limit (50)
                  How  many  simultaneous  connections  any client is
                  allowed to make to this service.

           smtpd_client_connection_rate_limit (0)
                  The  maximal  number  of  connection  attempts  any
                  client  is allowed to make to this service per time
                  unit.

           smtpd_client_message_rate_limit (0)
                  The maximal number  of  message  delivery  requests
                  that  any client is allowed to make to this service
                  per time unit, regardless of whether or not Postfix
                  actually accepts those messages.

           smtpd_client_recipient_rate_limit (0)
                  The  maximal number of recipient addresses that any
                  client is allowed to send to this service per  time
                  unit, regardless of whether or not Postfix actually
                  accepts those recipients.

           smtpd_client_event_limit_exceptions ($mynetworks)
                  Clients that are excluded  from  connection  count,
                  connection rate, or SMTP request rate restrictions.

           Available in Postfix version 2.3 and later:

           smtpd_client_new_tls_session_rate_limit (0)
                  The maximal number of new (i.e., uncached) TLS ses-
                  sions that a remote SMTP client is allowed to nego-
                  tiate with this service per time unit.

    TARPIT CONTROLS
           When a remote SMTP client makes errors, the  Postfix  SMTP
           server  can insert delays before responding. This can help
           to slow down run-away  software.   The  behavior  is  con-
           trolled  by  an  error  counter  that counts the number of
           errors within an SMTP session that a client makes  without
           delivering mail.

           smtpd_error_sleep_time (1s)
                  With Postfix version 2.1 and later: the SMTP server
                  response delay after a client has  made  more  than
                  $smtpd_soft_error_limit   errors,  and  fewer  than
                  $smtpd_hard_error_limit errors, without  delivering
                  mail.

           smtpd_soft_error_limit (10)
                  The  number  of  errors  a  remote  SMTP  client is
                  allowed to make without delivering mail before  the
                  Postfix SMTP server slows down all its responses.

           smtpd_hard_error_limit (20)
                  The  maximal  number of errors a remote SMTP client
                  is allowed to make without delivering mail.

           smtpd_junk_command_limit (100)
                  The number of junk commands (NOOP,  VRFY,  ETRN  or
                  RSET) that a remote SMTP client can send before the
                  Postfix SMTP server starts to increment  the  error
                  counter with each junk command.

           Available in Postfix version 2.1 and later:

           smtpd_recipient_overshoot_limit (1000)
                  The  number of recipients that a remote SMTP client
                  can send in excess  of  the  limit  specified  with
                  $smtpd_recipient_limit,  before  the  Postfix  SMTP
                  server increments the per-session error  count  for
                  each excess recipient.

    ACCESS POLICY DELEGATION CONTROLS
           As  of  version 2.1, Postfix can be configured to delegate
           access policy decisions to an external  server  that  runs
           outside  Postfix.   See  the  file SMTPD_POLICY_README for
           more information.

           smtpd_policy_service_max_idle (300s)
                  The time after which an idle SMTPD  policy  service
                  connection is closed.

           smtpd_policy_service_max_ttl (1000s)
                  The time after which an active SMTPD policy service
                  connection is closed.

           smtpd_policy_service_timeout (100s)
                  The time limit for connecting  to,  writing  to  or
                  receiving from a delegated SMTPD policy server.

    ACCESS CONTROLS
           The  SMTPD_ACCESS_README document gives an introduction to
           all the SMTP server access control features.

           smtpd_delay_reject (yes)
                  Wait until the RCPT TO  command  before  evaluating
                  $smtpd_client_restrictions,    $smtpd_helo_restric-
                  tions and $smtpd_sender_restrictions, or wait until
                  the      ETRN     command     before     evaluating
                  $smtpd_client_restrictions and $smtpd_helo_restric-
                  tions.

           parent_domain_matches_subdomains  (see  'postconf -d' out-
           put)
                  What   Postfix   features   match   subdomains   of
                  "domain.tld" automatically, instead of requiring an
                  explicit ".domain.tld" pattern.

           smtpd_client_restrictions (empty)
                  Optional  SMTP  server  access  restrictions in the
                  context of a client SMTP connection request.

           smtpd_helo_required (no)
                  Require that a remote SMTP client introduces itself
                  at  the  beginning of an SMTP session with the HELO
                  or EHLO command.

           smtpd_helo_restrictions (empty)
                  Optional restrictions that the Postfix SMTP  server
                  applies in the context of the SMTP HELO command.

           smtpd_sender_restrictions (empty)
                  Optional  restrictions that the Postfix SMTP server
                  applies in the context of the MAIL FROM command.

           smtpd_recipient_restrictions           (permit_mynetworks,
           reject_unauth_destination)
                  The  access  restrictions  that  the  Postfix  SMTP
                  server  applies  in the context of the RCPT TO com-
                  mand.

           smtpd_etrn_restrictions (empty)
                  Optional SMTP server  access  restrictions  in  the
                  context of a client ETRN request.

           allow_untrusted_routing (no)
                  Forward    mail   with   sender-specified   routing
                  (user[@%!]remote[@%!]site) from  untrusted  clients
                  to destinations matching $relay_domains.

           smtpd_restriction_classes (empty)
                  User-defined  aliases for groups of access restric-
                  tions.

           smtpd_null_access_lookup_key (<>)
                  The lookup key to be used in SMTP access(5)  tables
                  instead of the null sender address.

           permit_mx_backup_networks (empty)
                  Restrict  the  use  of  the  permit_mx_backup  SMTP
                  access feature to only  domains  whose  primary  MX
                  hosts match the listed networks.

           Available in Postfix version 2.0 and later:

           smtpd_data_restrictions (empty)
                  Optional  access restrictions that the Postfix SMTP
                  server applies in the context of the SMTP DATA com-
                  mand.

           smtpd_expansion_filter (see 'postconf -d' output)
                  What  characters are allowed in $name expansions of
                  RBL reply templates.

           Available in Postfix version 2.1 and later:

           smtpd_reject_unlisted_sender (no)
                  Request that the Postfix SMTP server  rejects  mail
                  from   unknown   sender  addresses,  even  when  no
                  explicit reject_unlisted_sender access  restriction
                  is specified.

           smtpd_reject_unlisted_recipient (yes)
                  Request  that  the Postfix SMTP server rejects mail
                  for  unknown  recipient  addresses,  even  when  no
                  explicit  reject_unlisted_recipient access restric-
                  tion is specified.

           Available in Postfix version 2.2 and later:

           smtpd_end_of_data_restrictions (empty)
                  Optional access restrictions that the Postfix  SMTP
                  server  applies  in the context of the SMTP END-OF-
                  DATA command.

    SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS
           Postfix  version  2.1  introduces  sender  and   recipient
           address  verification.   This  feature  is  implemented by
           sending probe email messages that are not actually  deliv-
           ered.   This  feature  is requested via the reject_unveri-
           fied_sender   and    reject_unverified_recipient    access
           restrictions.   The status of verification probes is main-
           tained by the verify(8) server.  See the file ADDRESS_VER-
           IFICATION_README  for  information  about how to configure
           and operate the Postfix sender/recipient address verifica-
           tion service.

           address_verify_poll_count (3)
                  How  many  times to query the verify(8) service for
                  the completion of an address  verification  request
                  in progress.

           address_verify_poll_delay (3s)
                  The  delay between queries for the completion of an
                  address verification request in progress.

           address_verify_sender ($double_bounce_sender)
                  The sender address to use in  address  verification
                  probes; prior to Postfix 2.5 the default was "post-
                  master".

           unverified_sender_reject_code (450)
                  The numerical Postfix  SMTP  server  response  code
                  when   a   sender   address   is  rejected  by  the
                  reject_unverified_sender restriction.

           unverified_recipient_reject_code (450)
                  The numerical Postfix SMTP server response  when  a
                  recipient address is rejected by the reject_unveri-
                  fied_recipient restriction.

    ACCESS CONTROL RESPONSES
           The following  parameters  control  numerical  SMTP  reply
           codes and/or text responses.

           access_map_reject_code (554)
                  The  numerical  Postfix  SMTP  server response code
                  when a client  is  rejected  by  an  access(5)  map
                  restriction.

           defer_code (450)
                  The  numerical  Postfix  SMTP  server response code
                  when a remote SMTP client request  is  rejected  by
                  the "defer" restriction.

           invalid_hostname_reject_code (501)
                  The  numerical  Postfix  SMTP  server response code
                  when the client HELO or EHLO command  parameter  is
                  rejected    by   the   reject_invalid_helo_hostname
                  restriction.

           maps_rbl_reject_code (554)
                  The numerical Postfix  SMTP  server  response  code
                  when a remote SMTP client request is blocked by the
                  reject_rbl_client,             reject_rhsbl_client,
                  reject_rhsbl_sender    or    reject_rhsbl_recipient
                  restriction.

           non_fqdn_reject_code (504)
                  The numerical Postfix SMTP server reply code when a
                  client     request     is     rejected    by    the
                  reject_non_fqdn_helo_hostname,
                  reject_non_fqdn_sender or reject_non_fqdn_recipient
                  restriction.

           plaintext_reject_code (450)
                  The numerical Postfix  SMTP  server  response  code
                  when  a  request  is  rejected by the reject_plain-
                  text_session restriction.

           reject_code (554)
                  The numerical Postfix  SMTP  server  response  code
                  when  a  remote  SMTP client request is rejected by
                  the "reject" restriction.

           relay_domains_reject_code (554)
                  The numerical Postfix  SMTP  server  response  code
                  when   a   client   request   is  rejected  by  the
                  reject_unauth_destination recipient restriction.

           unknown_address_reject_code (450)
                  The numerical Postfix  SMTP  server  response  code
                  when  a  sender or recipient address is rejected by
                  the         reject_unknown_sender_domain         or
                  reject_unknown_recipient_domain restriction.

           unknown_client_reject_code (450)
                  The  numerical  Postfix  SMTP  server response code
                  when a client without valid address <=>  name  map-
                  ping is rejected by the reject_unknown_client_host-
                  name restriction.

           unknown_hostname_reject_code (450)
                  The numerical Postfix  SMTP  server  response  code
                  when  the  hostname specified with the HELO or EHLO
                  command       is       rejected       by        the
                  reject_unknown_helo_hostname restriction.

           Available in Postfix version 2.0 and later:

           default_rbl_reply (see 'postconf -d' output)
                  The  default  SMTP  server  response template for a
                  request that is rejected by an  RBL-based  restric-
                  tion.

           multi_recipient_bounce_reject_code (550)
                  The  numerical  Postfix  SMTP  server response code
                  when a remote SMTP client request is blocked by the
                  reject_multi_recipient_bounce restriction.

           rbl_reply_maps (empty)
                  Optional lookup tables with RBL response templates.

    MISCELLANEOUS CONTROLS
           config_directory (see 'postconf -d' output)
                  The default location of  the  Postfix  main.cf  and
                  master.cf configuration files.

           daemon_timeout (18000s)
                  How  much time a Postfix daemon process may take to
                  handle a request  before  it  is  terminated  by  a
                  built-in watchdog timer.

           command_directory (see 'postconf -d' output)
                  The  location  of  all  postfix administrative com-
                  mands.

           double_bounce_sender (double-bounce)
                  The sender address of postmaster notifications that
                  are generated by the mail system.

           ipc_timeout (3600s)
                  The time limit for sending or receiving information
                  over an internal communication channel.

           mail_name (Postfix)
                  The mail system name that is displayed in Received:
                  headers,  in  the  SMTP  greeting  banner,  and  in
                  bounced mail.

           mail_owner (postfix)
                  The UNIX system account that owns the Postfix queue
                  and most Postfix daemon processes.

           max_idle (100s)
                  The  maximum  amount  of  time that an idle Postfix
                  daemon process waits  for  an  incoming  connection
                  before terminating voluntarily.

           max_use (100)
                  The  maximal  number of incoming connections that a
                  Postfix daemon process will service  before  termi-
                  nating voluntarily.

           myhostname (see 'postconf -d' output)
                  The internet hostname of this mail system.

           mynetworks (see 'postconf -d' output)
                  The  list  of "trusted" SMTP clients that have more
                  privileges than "strangers".

           myorigin ($myhostname)
                  The domain name that locally-posted mail appears to
                  come  from,  and that locally posted mail is deliv-
                  ered to.

           process_id (read-only)
                  The process ID  of  a  Postfix  command  or  daemon
                  process.

           process_name (read-only)
                  The  process  name  of  a Postfix command or daemon
                  process.

           queue_directory (see 'postconf -d' output)
                  The location of the Postfix top-level queue  direc-
                  tory.

           recipient_delimiter (empty)
                  The separator between user names and address exten-
                  sions (user+foo).

           smtpd_banner ($myhostname ESMTP $mail_name)
                  The text that follows the 220 status  code  in  the
                  SMTP greeting banner.

           syslog_facility (mail)
                  The syslog facility of Postfix logging.

           syslog_name (postfix)
                  The  mail  system  name  that  is  prepended to the
                  process name in syslog  records,  so  that  "smtpd"
                  becomes, for example, "postfix/smtpd".

           Available in Postfix version 2.2 and later:

           smtpd_forbidden_commands (CONNECT, GET, POST)
                  List  of  commands  that  causes  the  Postfix SMTP
                  server to immediately terminate the session with  a
                  221 code.

           Available in Postfix version 2.5 and later:

           smtpd_client_port_logging (no)
                  Enable  logging  of  the remote SMTP client port in
                  addition to the hostname and IP address.

    SEE ALSO
           anvil(8), connection/rate limiting
           cleanup(8), message canonicalization
           tlsmgr(8), TLS session and PRNG management
           trivial-rewrite(8), address resolver
           verify(8), address verification service
           postconf(5), configuration parameters
           master(5), generic daemon options
           master(8), process manager
           syslogd(8), system logging

    README FILES
           ADDRESS_CLASS_README, blocking unknown hosted or relay recipients
           ADDRESS_REWRITING_README Postfix address manipulation
           FILTER_README, external after-queue content filter
           LOCAL_RECIPIENT_README, blocking unknown local recipients
           MILTER_README, before-queue mail filter applications
           SMTPD_ACCESS_README, built-in access policies
           SMTPD_POLICY_README, external policy server
           SMTPD_PROXY_README, external before-queue content filter
           SASL_README, Postfix SASL howto
           TLS_README, Postfix STARTTLS howto
           VERP_README, Postfix XVERP extension
           XCLIENT_README, Postfix XCLIENT extension
           XFORWARD_README, Postfix XFORWARD extension

    LICENSE
           The  Secure  Mailer  license must be distributed with this
           software.

    AUTHOR(S)
           Wietse Venema
           IBM T.J. Watson Research
           P.O. Box 704
           Yorktown Heights, NY 10598, USA

           SASL support originally by:
           Till Franke
           SuSE Rhein/Main AG
           65760 Eschborn, Germany

           TLS support originally by:
           Lutz Jaenicke
           BTU Cottbus
           Allgemeine Elektrotechnik
           Universitaetsplatz 3-4
           D-03044 Cottbus, Germany

           Revised TLS support by:
           Victor Duchovni
           Morgan Stanley

                                                                          SMTPD(8)