SYNOPSIS
smtp [generic Postfix daemon options]
DESCRIPTION
The SMTP client processes message delivery requests from the queue man-
ager. 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 fin-
ished, 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 postmas-
ter 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.
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 pro-
cessor 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.
rency_limit)
The maximal number of parallel deliveries to the same destina-
tion via the smtp message delivery transport.
smtp_destination_recipient_limit ($default_destination_recipient_limit)
The maximal number of recipients per delivery via the smtp mes-
sage 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
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 proto-
col 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 con-
figuration 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 dae-
mon 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.
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, "post-
fix/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
SMTP(8)
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