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 recipient information. This program expects to be run from the master(8) process manager. The SMTP 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 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.

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)

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

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 commands 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 command.

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).

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 nesting level of multipart mail 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 XFORWARD 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 username:password entry per remote hostname or domain.

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

RESOURCE AND RATE CONTROLS

smtp_destination_concurrency_limit ($default_destination_concurrency_limit)
    The maximal number of parallel deliveries to the same destination via the smtp message delivery transport.

smtp_destination_recipient_limit ($default_destination_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 (120s)
    The SMTP client time limit for sending the RSET command, and for receiving the server response.

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 system receives mail on.

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 system 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 a connection.

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

SEE ALSO
qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
master(8), process manager
syslogd(8), system logging

README FILES
Use "postconf readme_directory" or "postconf html_directory" to locate this information.
SASL_README, Postfix SASL 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