Postfix manual - smtp(8)

    SMTP(8)                                                                SMTP(8)

    NAME
           smtp - Postfix SMTP client

    SYNOPSIS
           smtp [generic Postfix daemon options]

    DESCRIPTION
           The   Postfix   SMTP  client  processes  message  delivery
           requests from the queue manager. Each request specifies  a
           queue  file, a sender address, a domain or host to deliver
           to, and recipient information.  This program expects to be
           run from the master(8) process manager.

           The  SMTP  client updates the queue file and marks recipi-
           ents as finished, or it informs  the  queue  manager  that
           delivery  should  be tried again at a later time. Delivery
           status reports are sent  to  the  bounce(8),  defer(8)  or
           trace(8) daemon as appropriate.

           The  SMTP  client  looks  up  a  list  of  mail  exchanger
           addresses for the destination  host,  sorts  the  list  by
           preference,  and  connects to each listed address until it
           finds a server that responds.

           When a server is not  reachable,  or  when  mail  delivery
           fails  due  to  a  recoverable  error  condition, the SMTP
           client will try to deliver the mail to an alternate  host.

           After  a  successful mail transaction, a connection may be
           saved to the scache(8) connection cache server, so that it
           may  be  used by any SMTP client for a subsequent transac-
           tion.

           By default, connection caching is enabled temporarily  for
           destinations that have a high volume of mail in the active
           queue. Session caching can be enabled permanently for spe-
           cific destinations.

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

    STANDARDS
           RFC 821 (SMTP protocol)
           RFC 822 (ARPA Internet Text Messages)
           RFC 1651 (SMTP service extensions)
           RFC 1652 (8bit-MIME transport)
           RFC 1870 (Message Size Declaration)
           RFC 2045 (MIME: Format of Internet Message Bodies)
           RFC 2046 (MIME: Media Types)
           RFC 2554 (AUTH command)
           RFC 2821 (SMTP protocol)
           RFC 2920 (SMTP Pipelining)
           RFC 3207 (STARTTLS command)

    DIAGNOSTICS
           Problems  and transactions are logged to syslogd(8).  Cor-
           rupted message files are marked so that the queue  manager
           can move them to the corrupt queue for further inspection.

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

    BUGS
           SMTP connection caching does not work with TLS. The neces-
           sary  support for TLS object passivation and re-activation
           does not exist without closing the session, which  defeats
           the purpose.

           SMTP  connection caching assumes that SASL credentials are
           valid for all destinations  that  map  onto  the  same  IP
           address and TCP port.

    CONFIGURATION PARAMETERS
           Changes to main.cf are picked up automatically, as smtp(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
           ignore_mx_lookup_error (no)
                  Ignore DNS MX lookups that produce no response.

           smtp_always_send_ehlo (yes)
                  Always send EHLO at the start of an SMTP session.

           smtp_never_send_ehlo (no)
                  Never send EHLO at the start of an SMTP session.

           smtp_defer_if_no_mx_address_found (no)
                  Defer mail delivery when no MX record  resolves  to
                  an IP address.

           smtp_line_length_limit (990)
                  The maximal length of message header and body lines
                  that Postfix will send via SMTP.

           smtp_pix_workaround_delay_time (10s)
                  How long the  Postfix  SMTP  client  pauses  before
                  sending ".<CR><LF>" in order to work around the PIX
                  firewall "<CR><LF>.<CR><LF>" bug.

           smtp_pix_workaround_threshold_time (500s)
                  How long a message must be queued  before  the  PIX
                  firewall   "<CR><LF>.<CR><LF>"  bug  workaround  is
                  turned on.

           smtp_quote_rfc821_envelope (yes)
                  Quote addresses in SMTP MAIL FROM and RCPT TO  com-
                  mands as required by RFC 821.

           smtp_skip_5xx_greeting (yes)
                  Skip SMTP servers that greet with a 5XX status code
                  (go away, do not try again later).

           smtp_skip_quit_response (yes)
                  Do not wait for the response to the SMTP QUIT  com-
                  mand.

           Available in Postfix version 2.0 and earlier:

           smtp_skip_4xx_greeting (yes)
                  Skip SMTP servers that greet with a 4XX status code
                  (go away, try again later).

           Available in Postfix version 2.2 and later:

           smtp_discard_ehlo_keyword_address_maps (empty)
                  Lookup tables, indexed by the  remote  SMTP  server
                  address,  with  case insensitive lists of EHLO key-
                  words (pipelining, starttls, auth, etc.)  that  the
                  SMTP client will ignore in the EHLO response from a
                  remote SMTP server.

           smtp_discard_ehlo_keywords (empty)
                  A case insensitive list of EHLO keywords  (pipelin-
                  ing,  starttls,  auth,  etc.)  that the SMTP client
                  will ignore in the EHLO response from a remote SMTP
                  server.

           smtp_generic_maps (empty)
                  Optional lookup tables that perform address rewrit-
                  ing in the SMTP client, typically  to  transform  a
                  locally valid address into a globally valid address
                  when sending mail across the Internet.

    MIME PROCESSING CONTROLS
           Available in Postfix version 2.0 and later:

           disable_mime_output_conversion (no)
                  Disable the conversion of 8BITMIME format  to  7BIT
                  format.

           mime_boundary_length_limit (2048)
                  The  maximal  length  of  MIME  multipart  boundary
                  strings.

           mime_nesting_limit (100)
                  The maximal recursion level that the MIME processor
                  will handle.

    EXTERNAL CONTENT INSPECTION CONTROLS
           Available in Postfix version 2.1 and later:

           smtp_send_xforward_command (no)
                  Send  the  non-standard  XFORWARD  command when the
                  Postfix SMTP server EHLO response  announces  XFOR-
                  WARD support.

    SASL AUTHENTICATION CONTROLS
           smtp_sasl_auth_enable (no)
                  Enable  SASL  authentication  in  the  Postfix SMTP
                  client.

           smtp_sasl_password_maps (empty)
                  Optional SMTP client lookup tables with  one  user-
                  name:password  entry per remote hostname or domain.

           smtp_sasl_security_options (noplaintext, noanonymous)
                  What authentication  mechanisms  the  Postfix  SMTP
                  client is allowed to use.

           Available in Postfix version 2.2 and later:

           smtp_sasl_mechanism_filter (empty)
                  If  non-empty, a Postfix SMTP client filter for the
                  remote SMTP server's list of  offered  SASL  mecha-
                  nisms.

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

           smtp_use_tls (no)
                  Opportunistic mode: use  TLS  when  a  remote  SMTP
                  server  announces  STARTTLS support, otherwise send
                  the mail in the clear.

           smtp_enforce_tls (no)
                  Enforcement mode: require that remote SMTP  servers
                  use  TLS  encryption,  and  never  send mail in the
                  clear.

           smtp_sasl_tls_security_options           ($smtp_sasl_secu-
           rity_options)
                  The SASL authentication security options  that  the
                  Postfix  SMTP  client  uses  for TLS encrypted SMTP
                  sessions.

           smtp_starttls_timeout (300s)
                  Time limit for Postfix SMTP client write  and  read
                  operations  during  TLS  startup and shutdown hand-
                  shake procedures.

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

           smtp_tls_CApath (empty)
                  Directory with  PEM  format  certificate  authority
                  certificates  that  the Postfix SMTP client uses to
                  verify a remote SMTP server certificate.

           smtp_tls_cert_file (empty)
                  File with the Postfix SMTP client  RSA  certificate
                  in PEM format.

           smtp_tls_cipherlist (empty)
                  Controls  the Postfix SMTP client TLS cipher selec-
                  tion scheme.

           smtp_tls_dcert_file (empty)
                  File with the Postfix SMTP client  DSA  certificate
                  in PEM format.

           smtp_tls_dkey_file ($smtp_tls_dcert_file)
                  File  with  the Postfix SMTP client DSA private key
                  in PEM format.

           smtp_tls_enforce_peername (yes)
                  When TLS encryption is enforced, require  that  the
                  remote SMTP server hostname matches the information
                  in the remote SMTP server certificate.

           smtp_tls_key_file ($smtp_tls_cert_file)
                  File with the Postfix SMTP client RSA  private  key
                  in PEM format.

           smtp_tls_loglevel (0)
                  Enable  additional  Postfix  SMTP client logging of
                  TLS activity.

           smtp_tls_note_starttls_offer (no)
                  Log the hostname  of  a  remote  SMTP  server  that
                  offers  STARTTLS,  when  TLS is not already enabled
                  for that server.

           smtp_tls_per_site (empty)
                  Optional lookup tables with the Postfix SMTP client
                  TLS  usage  policy  by  next-hop domain name and by
                  remote SMTP server hostname.

           smtp_tls_scert_verifydepth (5)
                  The verification depth for remote SMTP server  cer-
                  tificates.

           smtp_tls_session_cache_database (empty)
                  Name  of  the  file containing the optional Postfix
                  SMTP client TLS session cache.

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

           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).

    RESOURCE AND RATE CONTROLS
           smtp_destination_concurrency_limit      ($default_destina-
           tion_concurrency_limit)
                  The maximal number of parallel  deliveries  to  the
                  same  destination  via  the  smtp  message delivery
                  transport.

           smtp_destination_recipient_limit        ($default_destina-
           tion_recipient_limit)
                  The maximal number of recipients per  delivery  via
                  the smtp message delivery transport.

           smtp_connect_timeout (30s)
                  The  SMTP  client  time  limit for completing a TCP
                  connection,  or  zero  (use  the  operating  system
                  built-in time limit).

           smtp_helo_timeout (300s)
                  The  SMTP client time limit for sending the HELO or
                  EHLO command, and for receiving the initial  server
                  response.

           smtp_xforward_timeout (300s)
                  The SMTP client time limit for sending the XFORWARD
                  command, and for receiving the server response.

           smtp_mail_timeout (300s)
                  The SMTP client time limit  for  sending  the  MAIL
                  FROM   command,   and   for  receiving  the  server
                  response.

           smtp_rcpt_timeout (300s)
                  The SMTP client time limit  for  sending  the  SMTP
                  RCPT  TO  command,  and  for  receiving  the server
                  response.

           smtp_data_init_timeout (120s)
                  The SMTP client time limit  for  sending  the  SMTP
                  DATA   command,   and   for  receiving  the  server
                  response.

           smtp_data_xfer_timeout (180s)
                  The SMTP client time limit  for  sending  the  SMTP
                  message content.

           smtp_data_done_timeout (600s)
                  The  SMTP  client  time  limit for sending the SMTP
                  ".", and for receiving the server response.

           smtp_quit_timeout (300s)
                  The SMTP client time limit  for  sending  the  QUIT
                  command, and for receiving the server response.

           Available in Postfix version 2.1 and later:

           smtp_mx_address_limit (0)
                  The  maximal  number  of  MX  (mail  exchanger)  IP
                  addresses  that  can  result  from  mail  exchanger
                  lookups, or zero (no limit).

           smtp_mx_session_limit (2)
                  The  maximal  number  of SMTP sessions per delivery
                  request before giving up or delivering to  a  fall-
                  back relay host, or zero (no limit).

           smtp_rset_timeout (20s)
                  The  SMTP  client  time  limit for sending the RSET
                  command, and for receiving the server response.

           Available in Postfix version 2.2 and later:

           smtp_connection_cache_destinations (empty)
                  Permanently enable SMTP connection caching for  the
                  specified destinations.

           smtp_connection_cache_on_demand (yes)
                  Temporarily  enable SMTP connection caching while a
                  destination has a high volume of mail in the active
                  queue.

           smtp_connection_cache_reuse_limit (10)
                  When SMTP connection caching is enabled, the number
                  of times that an SMTP session is reused  before  it
                  is closed.

           smtp_connection_cache_time_limit (2s)
                  When SMTP connection caching is enabled, the amount
                  of time that an unused SMTP client socket  is  kept
                  open before it is closed.

    TROUBLE SHOOTING CONTROLS
           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.

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

    MISCELLANEOUS CONTROLS
           best_mx_transport (empty)
                  Where  the  Postfix SMTP client should deliver mail
                  when it detects a "mail loops back to myself" error
                  condition.

           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.

           disable_dns_lookups (no)
                  Disable DNS lookups in the Postfix  SMTP  and  LMTP
                  clients.

           fallback_relay (empty)
                  Optional  list of relay hosts for SMTP destinations
                  that can't be found or that are unreachable.

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

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

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

           max_idle (100s)
                  The  maximum  amount  of  time that an idle Postfix
                  daemon process waits for the next  service  request
                  before exiting.

           max_use (100)
                  The  maximal number of connection requests before a
                  Postfix daemon process terminates.

           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.

           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.

           smtp_bind_address (empty)
                  An optional numerical network address that the SMTP
                  client  should  bind to when making an IPv4 connec-
                  tion.

           smtp_bind_address6 (empty)
                  An optional numerical network address that the SMTP
                  client  should  bind to when making an IPv6 connec-
                  tion.

           smtp_helo_name ($myhostname)
                  The hostname to send in the SMTP EHLO or HELO  com-
                  mand.

           smtp_host_lookup (dns)
                  What  mechanisms  when the SMTP client uses to look
                  up a host's IP address.

           smtp_randomize_addresses (yes)
                  Randomize the order  of  equal-preference  MX  host
                  addresses.

           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".

    SEE ALSO
           qmgr(8), queue manager
           bounce(8), delivery status reports
           scache(8), connection cache server
           postconf(5), configuration parameters
           master(5), generic daemon options
           master(8), process manager
           tlsmgr(8), TLS session and PRNG management
           syslogd(8), system logging

    README FILES
           SASL_README, Postfix SASL howto
           TLS_README, Postfix STARTTLS howto

    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

           Command pipelining in cooperation with:
           Jon Ribbens
           Oaktree Internet Solutions Ltd.,
           Internet House,
           Canal Basin,
           Coventry,
           CV1 4LY, United Kingdom.

           Connection caching in cooperation with:
           Victor Duchovni
           Morgan Stanley

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

                                                                           SMTP(8)