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SMTP(8)                                                                SMTP(8)

NAME
       smtp - Postfix SMTP+LMTP client

SYNOPSIS
       smtp [generic Postfix daemon options]

DESCRIPTION
       The  Postfix SMTP+LMTP client implements the SMTP and LMTP
       mail delivery protocols.  It  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+LMTP client updates  the  queue  file  and  marks
       recipients  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+LMTP 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+LMTP
       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+LMTP  client  for  a  subsequent
       transaction.

       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.

SMTP DESTINATION SYNTAX
       SMTP destinations have the following form:

       domainname, domainname:port
              Look up  the  mail  exchangers  for  the  specified
              domain.

       [hostname], [hostname]:port
              Look up the address of the specified host.

       [address], [address]:port
              Connect  to  the  host at the specified address. An
              IPv6 address must be formatted as [ipv6:address].

       In all the above cases, when no port is specified, look up
       the port defined as smtp in services(4).

LMTP DESTINATION SYNTAX
       LMTP destinations have the following form:

       unix:pathname
              Connect  to  the  local  UNIX-domain server that is
              bound to the specified  pathname.  If  the  process
              runs  chrooted, an absolute pathname is interpreted
              relative to the Postfix queue directory.

       inet:hostname, inet:hostname:port

       inet:[address], inet:[address]:port
              Connect to the specified TCP port on the  specified
              local or remote host. If no port is specified, con-
              nect to the port defined as  lmtp  in  services(4).
              If no such service is found, the lmtp_tcp_port con-
              figuration parameter (default value of 24) will  be
              used.

SECURITY
       The  SMTP+LMTP client is moderately security-sensitive. It
       talks to SMTP or LMTP servers and to DNS  servers  on  the
       network. The SMTP+LMTP 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 2033 (LMTP protocol)
       RFC 2034 (Enhanced Status Codes)
       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)
       RFC 3463 (Enhanced Status Codes)

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

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

CONFIGURATION PARAMETERS
       Most smtp_xxx configuration parameters  have  an  lmtp_xxx
       "ghost"  parameter  for  the equivalent LMTP feature. This
       document describes only those LMTP-related parameters that
       aren't simply "ghost" 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.

       Available in Postfix version 2.3 and later:

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

       lmtp_discard_lhlo_keywords ($myhostname)
              A case insensitive list of LHLO keywords  (pipelin-
              ing,  starttls,  auth,  etc.)  that the LMTP client
              will ignore in the LHLO response from a remote LMTP
              server.

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,
              or sender address when sender-dependent authentica-
              tion is enabled.

       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.

       Available in Postfix version 2.3 and later:

       smtp_sender_dependent_authentication (no)
              Enable  sender-dependent authentication in the SMTP
              client; this is available only with SASL  authenti-
              cation,  and  disables  SMTP  connection caching to
              ensure that mail from different  senders  will  use
              the appropriate credentials.

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.

       lmtp_lhlo_timeout (300s)
              The  LMTP  client  time  limit for sending the LHLO
              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 (5)
              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_reuse_time_limit (300s)
              The amount of time during which Postfix will use an
              SMTP connection repeatedly.

       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.

       delay_logging_resolution_limit (2)
              The  maximal  number  of  digits  after the decimal
              point when logging sub-second delay values.

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

       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.

       lmtp_tcp_port (24)
              The default TCP port that the Postfix  LMTP  client
              connects to.

       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.

       lmtp_lhlo_name ($myhostname)
              The hostname to send in the LMTP LHLO command.

       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".

       Available with Postfix 2.2 and earlier:

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

       Available with Postfix 2.3 and later:

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

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.

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

       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)