sendmail — Send an E-mail message
sendmail [option...] [--] [address...]
rmail [-f sender] {address} [address...]
The sendmail command reads an E-mail message and delivers the message to its recipients. This sendmail command is part of the Courier mail server, although it attempts to emulate the behavior of the original sendmail MTA. Applications written for Sendmail should be able to use Courier mail server's sendmail. This sendmail wrapper understands most command line arguments used by sendmail 8.9. Certain sendmail-specific arguments that make no sense for Courier, (like -o), are silently ignored.
This sendmail always behaves like the real sendmail with the
-oi and -t options. This is how most
applications expect it to work. Some applications might run sendmail without
the -oi and -t options, and expect
sendmail's legacy
behavior when those options are not used. Those application may have problems
with this sendmail wrapper.
sendmail reads the message from standard input, rewrites its headers appropriately and delivers it to the specified recipients.
If at least one E-mail address is specified on the command line,
sendmail delivers the message to those recipients only.
If no
addresses are specified on the command line, sendmail
reads the
message and builds the recipient list from the To:,
Cc: and Bcc: headers.
sendmail always removes Bcc:
headers before sending the message if recipients are not specified on the
command line.
Some of the functionality described below is actually implemented by other Courier modules that sendmail runs automatically. This process is transparent to the end user, or the application.
-f address
Sets the From: address. This is just
the E-mail address only, not the name.
-F "name"
Sets the name to put in the From: header.
-N options
Sets delivery status notification
options. options is a comma-separated list of one or more of the
following keywords: never, success,
fail, delay. If not specified, the
-N option
defaults to either "delay, fail", or just
"fail", depending on systemwide options set by the
administrator. The "success" keyword sends a return receipt
to the sender when the message is succesfully received by each recipient.
"fail" sends a notice if the message could not be delivered
for some reason. "delay" sends a notice if the message
remains undeliverable for a period of time (but has not yet completely
failed). "never" means do not send any notices for any
reason, but see BUGS below.
-nDo not actually deliver the message, but copy it to standard output, after rewriting all the headers.
-o, -t, -qThese sendmail-specific options are ignored, because this is not the real sendmail.
-R fullRequests that delivery status notifications include the original message, in its entirety.
-R hdrsRequests that delivery status notifications include just the headers of the original message.
-V "envid"Specifies the original envelope id to be returned in delivery status notifications. Of interest only to mail robots.
-S "level"
Specify level as a minimum
security level for delivering this message. This is a Courier-specific
extension that uses a Courier-specific SMTP extension. level is
either "NONE" or "STARTTLS". "NONE" specifies the normal security level
(none at all); "STARTTLS" specifies that SSL/TLS must be used when
transmitting this message to a remote mail relay, and the remote mail
relay must supply a certificate that's signed by a private certificate authority
that's configured in Courier. See Courier installation notes for more
information.
-bcc
Read Bcc: headers only. Normally, if no
recipients are specified, sendmail obtains the list of
recipients by reading the To:, Cc: and
Bcc: headers (Bcc: headers are then
removed).
The -bcc option ignores To: and
Cc:
headers for this purpose. This option is ignored if an explicit address
list is specified on the sendmail command line.
-bsTalk ESMTP on standard input. This option is actually implemented by running Courier's ESMTP server, which takes over and provides a complete ESMTP implementation.
-verp
Use a VERP for this message.
The return address is the E-mail address where delivery status notifications (non-delivery notices, or return receipts) are sent for this message.
sendmail constructs the envelope sender (the return address),
userid@host as follows, unless the -bs
option was
specified. If the -bs option is specified the envelope sender is
specified via ESMTP commands, of course.
If the -f option was specified, the address specified by the
-f option is used.
Otherwise, the userid portion of the return address is set to
the contents of the first environment variable that's defined from the
following list: MAILSUSER, MAILUSER,
LOGNAME, LOGUSER. If none of these environment
variables are defined, the system account name is used.
The host portion of the return address is set to the contents
of the MAILSHOST environment variable. If
MAILSHOST
is not defined, MAILHOST will be used. If neither variable is
set, the configured machine name is used.
The return address is then subject to the address rewriting rules for the
"local" Courier module (the "esmtp" module when the -bs flag is
specified).
Finally, if the -verp option was specified, the return address
is VERPed.
A VERP is a return address which contains the recipient address encoded in it. Not all MTAs support RFC 1894-based delivery status notifications. VERPs permit mailing list software to identify non-deliverable addresses even in the absence of a machine-readable DSN.
This option exists mainly to support Courier's own mailing list manager. At this time, it's the only software in the world that knows how to use this option. The Qmail server originally had very similar functionality, for it's own mailing list manager. However, there are many functional differences between the two mail servers, so Courier mail server's and Qmail's mailing list managers are not interchangeable.
Except for this detail,
Courier's implementation of a VERP is very similar to
Qmail's. When a message from user@domain.com is addressed to
address X, then return address will be set to user-Y@domain.com,
where Y is defined as follows:
1. The last @ character in X is changed to the = character.
2. The remaining characters in X are copied verbatim to Y, except for some special characters like @, +, %, :, and !.
3. These special characters are replaced with the character +, followed by a two-character hexadecimal ASCII code for the special character.
Using -verp for a message to multiple recipients results in
Courier generating and transmitting one copy of the message separately to
every recipient. That's because the return address for every recipient is
different, requiring a separate message to be sent.
Except in one case.
The one exception is when a VERPed message is sent from one Courier server
to another Courier server via ESMTP. An ESMTP extension will be used to send
one message, preserving the VERP status of the message. This ESMTP extension
is described in the document,
draft-varshavchik-verp-smtpext,
a copy of which is included in Courier's source code.
sendmail sets the contents of the
From: header as
follows. Note that this is not the same as the return address of the
message.
If the -bs option is specified, none of the following will be
applicable. All environment variables are ignored when the -bs
option is used.
If the From: header is present in the message, but the
environment variable MAILUSER is set, the userid portion of the
From: header is replaced by the contents of
MAILUSER.
If the From: header is present in the message, but the
MAILHOST environment variable is set, the contents of
MAILHOST replaces the host portion of the
From: header.
If the From: header is present in the message,
but either the
-F option was specified, or the MAILNAME or the
NAME environment variable is set, the contents of the -F option,
or the environment variable, will replace the sender's name in the
From: header.
If the From: header is not present in the message, one is
constructed as follows. The sender's name is set by the -F option. If the -F
option was not specified, the contents of the MAILNAME or the
NAME environment variable is used. If neither variable is used,
the name is looked up from the system account file. The userid portion of the
address is set by the contents of any one of the following environment
variables: MAILUSER, LOGNAME,
USER. If none of these variables
are set, the system userid is used. The host portion of the address is set by
the contents of the MAILHOST environment variable. If it is not
set, the system name of the server is used.
sendmail exits with exit status of zero if the message was
succesfully scheduled for a delivery. If there was a problem accepting the
message for delivery, sendmail displays an error message and
exits with a non-zero status. The exit status will always be zero when the
-bs option is used,
unless a serious system problem occurs.
If called as rmail, only a subset of these options are
available, namely -f, -verp,
-N, -R, -V,
-o, and -t. Other options are not
allowed. Additionally, recipient addresses must be explicitly specified on the
command line. The rmail alias is intended to be used for
receiving mail via UUCP. You must install compatible UUCP software separately,
and set it up so that it looks for rmail in Courier's
installation directory.
When invoked as rmail this wrapper will refuse to run unless
it is invoked by the uucp user. Additionally, the
UU_MACHINE and UU_USER environment
variables must be
defined. Also, header and address rewriting described in previous paragraphs
do not take place; instead, UUCP-specific header and address rewriting rules
will apply. See the
courieruucp(8)
manual page for more information.
There are still some mail gateways out there that do not implement
delivery status notifications according to RFC 1894. This means that you may
get a delivery notice even if -N never keyword was
specified.
Header rewriting rules are similar, but not identical, to Qmail's. The precedence of the various environment variables, plus the situations where they're used, are different from Qmail's and may produce different results.