    SMTP(8)                                                   SMTP(8)

    NAME
           smtp - Postfix remote delivery via SMTP

    SYNOPSIS
           smtp [generic Postfix daemon options]

    DESCRIPTION
           The  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 recip-
           ient 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
           problem reports are sent to the bounce(8) or defer(8) dae-
           mon 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 the domain or host is specified as a comma/whitespace
           separated  list, the SMTP client repeats the above process
           for  all  destinations  until  it  finds  a  server   that
           responds.

           Once the SMTP client has received the server greeting ban-
           ner, no error will cause it to proceed to the next address
           on the mail exchanger list. Instead, the message is either
           bounced, or its delivery is deferred until later.

    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 1651 (SMTP service extensions)
           RFC 1870 (Message Size Declaration)
           RFC 2197 (Pipelining)
           RFC 2554 (AUTH 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.

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    SMTP(8)                                                   SMTP(8)

    BUGS
    CONFIGURATION PARAMETERS
           The  following  main.cf parameters are especially relevant
           to this program. See the Postfix main.cf file  for  syntax
           details  and  for  default  values. Use the postfix reload
           command after a configuration change.

    Miscellaneous
           best_mx_transport
                  Name of the delivery  transport  to  use  when  the
                  local  machine is the most-preferred mail exchanger
                  (by default, a mailer loop  is  reported,  and  the
                  message is bounced).

           debug_peer_level
                  Verbose  logging  level  increment  for  hosts that
                  match a pattern in the debug_peer_list parameter.

           debug_peer_list
                  List of domain or network patterns. When  a  remote
                  host  matches  a pattern, increase the verbose log-
                  ging  level  by  the  amount   specified   in   the
                  debug_peer_level parameter.

           disable_dns_lookups
                  Disable  DNS  lookups. This means that mail must be
                  forwarded via a smart relay host.

           error_notice_recipient
                  Recipient   of    protocol/policy/resource/software
                  error notices.

           fallback_relay
                  Hosts  to hand off mail to if a message destination
                  is not found or if a destination is unreachable.

           ignore_mx_lookup_error
                  When a name server fails to respond to an MX query,
                  search  for  an  A  record  instead  deferring mail
                  delivery.

           inet_interfaces
                  The network interface addresses that this mail sys-
                  tem  receives  mail on. When any of those addresses
                  appears in the list of mail exchangers for a remote
                  destination,  the  list  is truncated to avoid mail
                  delivery loops.

           notify_classes
                  When this parameter includes  the  protocol  class,
                  send  mail  to  the  postmaster with transcripts of
                  SMTP sessions with protocol errors.

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    SMTP(8)                                                   SMTP(8)

           smtp_always_send_ehlo
                  Always send EHLO at the start of a connection.

           smtp_never_send_ehlo
                  Never send EHLO at the start of a connection.

           smtp_skip_4xx_greeting
                  Skip servers that greet us with a 4xx status  code.

           smtp_skip_5xx_greeting
                  Skip  servers that greet us with a 5xx status code.

           smtp_skip_quit_response
                  Do not wait for the server response  after  sending
                  QUIT.

           smtp_bind_address
                  Numerical  network address to bind to when making a
                  connection.

    Authentication controls
           smtp_enable_sasl_auth
                  Enable per-session authentication as per  RFC  2554
                  (SASL).   By default, Postfix is built without SASL
                  support.

           smtp_sasl_password_maps
                  Lookup tables with per-host or domain name:password
                  entries.   No  entry for a host means no attempt to
                  authenticate.

           smtp_sasl_security_options
                  Zero or more of the following.

                  noplaintext
                         Disallow  authentication  methods  that  use
                         plaintext passwords.

                  noactive
                         Disallow  authentication  methods  that  are
                         vulnerable to non-dictionary active attacks.

                  nodictionary
                         Disallow  authentication  methods  that  are
                         vulnerable to passive dictionary attack.

                  noanonymous
                         Disallow anonymous logins.

    Resource controls
           smtp_destination_concurrency_limit
                  Limit the number of parallel deliveries to the same
                  destination.   The  default limit is taken from the
                  default_destination_concurrency_limit parameter.

                                                                    3

    SMTP(8)                                                   SMTP(8)

           smtp_destination_recipient_limit
                  Limit the number of recipients per  message  deliv-
                  ery.    The   default   limit  is  taken  from  the
                  default_destination_recipient_limit parameter.

    Timeout controls
           The default time unit is seconds; an  explicit  time  unit
           can  be  specified by appending a one-letter suffix to the
           value: s (seconds), m (minutes), h (hours), d (days) or  w
           (weeks).

           smtp_connect_timeout
                  Timeout  for  completing  a TCP connection. When no
                  connection can be made  within  the  deadline,  the
                  SMTP  client  tries  the  next  address on the mail
                  exchanger list.

           smtp_helo_timeout
                  Timeout for receiving  the  SMTP  greeting  banner.
                  When  the server drops the connection without send-
                  ing a greeting banner, or when it sends no greeting
                  banner  within  the deadline, the SMTP client tries
                  the next address on the mail exchanger list.

           smtp_helo_timeout
                  Timeout for  sending  the  HELO  command,  and  for
                  receiving the server response.

           smtp_mail_timeout
                  Timeout  for sending the MAIL FROM command, and for
                  receiving the server response.

           smtp_rcpt_timeout
                  Timeout for sending the RCPT TO  command,  and  for
                  receiving the server response.

           smtp_data_init_timeout
                  Timeout  for  sending  the  DATA  command,  and for
                  receiving the server response.

           smtp_data_xfer_timeout
                  Timeout for sending the message content.

           smtp_data_done_timeout
                  Timeout  for  sending  the  "."  command,  and  for
                  receiving  the server response. When no response is
                  received, a warning is logged that the mail may  be
                  delivered multiple times.

           smtp_quit_timeout
                  Timeout  for  sending  the  QUIT  command,  and for
                  receiving the server response.

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    SMTP(8)                                                   SMTP(8)

    SEE ALSO
           bounce(8) non-delivery status reports
           master(8) process manager
           qmgr(8) queue manager
           syslogd(8) system logging

    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

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