sendmail - an electronic mail transport agent


/usr/sbin/sendmail [flag[...]] [address[...]] [-v]


The sendmail utility sends a message to one or more recipients identified by address, routing the message over whatever networks are necessary. The sendmail utility does internetwork forwarding as necessary to deliver the message to the correct destination.

The sendmail utility is not intended as a user interface routine; other programs provide user-friendly front ends. The sendmail utility is used only to deliver preformatted messages.

The -bd and -bD flags are not supported in this version of Windows Services for UNIX.

With no flags, sendmail reads its standard input up to an end-of-file or a line consisting only of a single dot and sends a copy of the message found there to all of the addresses listed. It determines one or more networks to use based on the syntax and contents of the addresses.

Local addresses are looked up in a file and aliased appropriately. Aliasing can be prevented by preceding the address with a backslash (\). Beginning with 8.10, the sender is included in any alias expansions. For instance, if 'john' sends to 'group', and 'group' includes 'john' in the expansion, the letter will also be delivered to 'john'.

In aliases, the first character of a name can be a vertical bar (|) to cause interpretation of the rest of the name as a command to pipe the mail to. It might be necessary to quote the name to keep sendmail from suppressing the blanks from between arguments. For example, a common alias is as follows:

msgs: "|/usr/bin/msgs -s"

Aliases can also have the syntax :include:filename to ask sendmail to read the named file for a list of recipients. For example, an alias such as the following would read /usr/local/lib/poets.list for the list of addresses making up the group:

poets: ":include:/usr/local/lib/poets.list"

If invoked as hoststat, sendmail will print the persistent host status database. If invoked as purgestat, sendmail will purge expired entries from the persistent host status database.


Set the body type to type. Current legal values 7BIT or 8BITMIME.
Go into ARPANET mode. All input lines must end with a CR-LF, and all messages will be generated with a CR-LF at the end. Also, the "From:" and "Sender:" fields are examined for the name of the sender.
Run as a daemon. This requires Berkeley interprocess communication (IPC). The sendmail utility will fork and run in background, listening on socket 25 for incoming Simple Mail Transfer Protocol (SMTP) connections. By default, sendmail will also listen on socket 587 for RFC2476 message submission. This is normally run from /etc/rc.
Same as -bd except runs in foreground.
Print the persistent host status database.
Purge expired entries from the persistent host status database.
Initialize the alias database.
Deliver mail in the usual way (default).
Print a listing of the queue.
Use the SMTP protocol as described in RFC821 on standard input and output. This flag implies all the operations of the -ba flag that are compatible with SMTP.
Run in address test mode. This mode reads addresses and shows the steps in parsing; it is used for debugging configuration tables.
Verify names only; do not try to collect or deliver a message. Verify mode is normally used for validating users or mailing lists.
Use alternate configuration file. The sendmail utility will not run as root if an alternate configuration file is specified.
Set debugging value to X.
Set the full name of the sender.
Sets the name of the "from" person (that is, the envelope sender of the mail). This address can also be used in the From: header if that header is missing during initial submission. The envelope sender address is used as the recipient for delivery status notifications and can also appear in a Return-Path: header. -f should only be used by trusted users (normally, root, daemon, and network) or if the person you are trying to become is the same as the person you are. Otherwise, an X-Authentication-Warning header will be added to the message.
Relay (gateway) submission of a message, such as when rmail calls sendmail.
Set the hop count to N. The hop count is incremented every time the mail is processed. When it reaches a limit, the mail is returned with an error message, the victim of an aliasing loop. If not specified, Received: lines in the message are counted.
Ignore dots alone on lines by themselves in incoming messages. This should be set if you are reading data from a file.
-L tag
Set the identifier used in syslog messages to the supplied tag.
-N dsn
Set delivery status notification conditions to dsn, which can be 'never' for no notifications or a comma-separated list of the values 'failure' to be notified if delivery failed, 'delay' to be notified if delivery is delayed, and 'success' to be notified when the message is successfully delivered.
Do not do aliasing.
-O option=value
Set option option to the specified value. This form uses long names.
-ox value
Set option x to the specified value. This form uses single character names only. The short names are not described in this topic; see the Sendmail Installation and Operation Guide for details.
Set the name of the protocol used to receive the message. This can be a simple protocol name such as UUCP or a protocol and hostname, such as UUCP:ucbvax.
Processed saved messages in the queue at given intervals. If time is omitted, process the queue once. Time is given as a tagged number, with 's' being seconds, 'm' being minutes, 'h' being hours, 'd' being days, and 'w' being weeks. For example, either '-q1h30m' or '-q90m' would set the timeout to one hour thirty minutes. If time is specified, sendmail will run in background. This option can be used safely with -bd.
Limit processed jobs to those containing substr as a substring of the queue identifier.
Limit processed jobs to those containing substr as a substring of one of the recipients.
Limit processed jobs to those containing substr as a substring of the sender.
-R return
Set the amount of the message to be returned if the message bounces. The return parameter can be 'full' to return the entire message or 'hdrs' to return only the headers. In the latter case, local bounces also return only the headers.
An alternate and obsolete form of the -f flag.
Read message for recipients. To:, Cc:, and Bcc: lines will be scanned for recipient addresses. The Bcc: line will be deleted before transmission.
Initial (user) submission. This should always be set when called from a user agent such as Mail or exmh and never be set when called by a network delivery agent such as rmail.
-V envid
Set the original envelope identifier. This is propagated across SMTP to servers that support DSNs and is returned in DSN-compliant error messages.
Go into verbose mode. Alias expansions will be announced.
-X logfile
Log all traffic in and out of mailers in the indicated log file. This should only be used as a last resort for debugging mailer bugs. It will log a lot of data very quickly.
Stop processing command flags and use the rest of the arguments as addresses.


There are also a number of processing options that can be set. Normally, these will only be used by a system administrator. Options can be set either on the command line using the -o flag (for short names), the -O flag (for long names) or in the configuration file. This is a partial list limited to those options that are likely to be useful on the command line and only shows the long names. For a complete list (and details), consult the Sendmail Installation and Operation Guide.

The options are:

Use alternate alias file.
On mailers that are considered expensive to connect to, do not initiate immediate connection. This requires queueing.
Checkpoint the queue file after every N successful deliveries (the default is ten). This prevents excessive duplicate deliveries when sending to long mailing lists interrupted by system crashes.
Set the delivery mode to x. Delivery modes are `i' for interactive (synchronous) delivery; `b' for background (asynchronous) delivery; `q' for queue only - that is, actual delivery is done the next time the queue is run; and `d' for deferred, which is the same as `q' except that database lookups for maps that have set the -D option (default for the host map) are avoided.
Set error processing to mode x. Valid modes are `m' to mail back the error message, `w' to write back the error message (or mail it back if the sender is not logged in), `p' to print the errors on the terminal (default), `q' to throw away error messages (only exit status is returned), and `e' to do special processing for the BerkNet. If the text of the message is not mailed back by modes `m' or `w', and if the sender is local to this computer, a copy of the message is appended to the file dead.letter in the sender's home directory.
Save UNIX-style From lines at the front of messages.
The maximum number of times a message is allowed to "hop" before we decide it is in a loop.
Do not take dots on a line by themselves as a message terminator.
Send error messages in MIME format. If not set, the DSN (Delivery Status Notification) SMTP extension is disabled.
Set connection cache timeout.
Set connection cache size.
The log level.
Do not send to "me" (the sender) if I am in an alias expansion.
Validate the right-hand side of aliases during a newaliases(1) command.
If set, this message might have old style headers. If not set, this message is guaranteed to have new style headers (that is, commas instead of spaces between addresses). If set, an adaptive algorithm is used that will correctly determine the header format in most cases.
Select the directory in which to queue messages.
Save statistics in the named file.
Set the timeout on undelivered messages in the queue to the specified time. After delivery has failed (for instance, because of a host being down) for this amount of time, failed messages will be returned to the sender. The default is five days.
If set, a user database is consulted to get forwarding information. You can consider this an adjunct to the aliasing mechanism, except that the database is intended to be distributed; aliases are local to a particular host. This might not be available if your sendmail does not have the USERDB option compiled in.
Fork each job during queue runs. Might be convenient on memory-poor computers.
Strip incoming messages to seven bits.
Set the handling of eight-bit input to seven-bit destinations to mode: m (mimefy) will convert to seven-bit MIME format, p (pass) will pass it as eight bits (but violates protocols), and s (strict) will bounce the message.
Sets how long a job must ferment in the queue between attempts to send it.
Sets the default character set used to label eight-bit data that is not otherwise labelled.
If opening a connection fails, sleep for sleeptime seconds and try again. Useful on dial-on-demand sites.
Set the behavior when there are no recipient headers (To:, Cc: or Bcc:) in the message to action: none leaves the message unchanged, add-to adds a To: header with the envelope recipients, add-apparently-to adds an Apparently-To: header with the envelope recipients, add-bcc adds an empty Bcc: header, and add-to-undisclosed adds a header reading `To: undisclosed-recipients:;'.
Sets the maximum number of children that an incoming SMTP daemon will allow to spawn at any time to N.
Sets the maximum number of connections per second to the SMTP port to N.


The sendmail utility returns an exit status describing what it did. The codes are defined in <sysexits.h>:

Successful completion on all addresses.
Username not recognized.
Catchall meaning necessary resources were not available.
Syntax error in address.
Internal software error, including bad arguments.
Temporary operating system error, such as "cannot fork."
Host name not recognized.
Message could not be sent immediately, but was queued.


Text file containing e-mail aliases; used by sendmail
Text file containing help information for sendmail; used by sendmail
Text file containing configuration file for sendmail
Data file containing statistical information about sendmail operations


Microsoft Windows Services for UNIX version 3.0 includes the sendmail package of utilities (version 8.11.6) as part of the base utilities. The primary purpose of including sendmail is to support scripting applications in which e-mail is sent by UNIX scripts that have been built using the tools included in Windows Services for UNIX 3.0.

Microsoft will support the use of sendmail only as an e-mail transport agent and not as a primary e-mail server. If you need an e-mail server, it is recommended that you use Microsoft Exchange Server.

The sendmail utility often gets blamed for many problems that are actually the result of other problems, such as overly permissive modes on directories. For this reason, sendmail checks the modes on system directories and files to determine whether they can be trusted. Although these checks can be turned off and your system security reduced by setting the DontBlameSendmail option, the permission problems should be fixed. For more information, see:

By default, Interix does not execute files with the set-user-ID (setuid) or set-group-ID (setgid) mode bit set for security reasons. If an attempt is made to execute such a file, the ENOSETUID error is returned. For more information and and instructions for enabling execution of files with these mode bits set, see The superuser account and appropriate privileges in Windows Services for UNIX Help.








Sendmail Installation and Operation Guide, No. 8, SMM.