SMTP relaying in sendmail

NOTE. As of October 2010, I use Postfix on Mac OS X, which is hilariously simpler to configure for this same task than sendmail. These instructions should still work, but I certainly won’t be updating them if I can help it.

Install SASL, which sendmail needs to authenticate at the SMTP relay.
```
 portinstall security/cyrus-sasl2
```
If you don’t already have the src distributions, install them now via sysinstall(8).

Recompile sendmail with SASL.

 cat >> /etc/make.conf
     SENDMAIL_CFLAGS=-I/usr/local/include/sasl -DSASL
     SENDMAIL_LDFLAGS=-L/usr/local/lib
     SENDMAIL_LDADD=-lsasl2
     ^D

 cd /usr/src/lib/libsmutil
 make cleandir && make obj && make
 cd /usr/src/lib/libsm
 make cleandir && make obj && make
 cd /usr/src/usr.sbin/sendmail
 make cleandir && make obj && make && make install

If you want to allow a subnet to relay mail through this machine, add it to the access database.

 cat >> /etc/mail/access
     Connect:192.168 RELAY
     ^D
 makemap hash /etc/mail/access < /etc/mail/access

Record the credentials sendmail will use to authenticate at the SMTP relay. Replace mail.panix.com with your SMTP relay’s hostname; cfm@panix.com, your username; *****, your password.

 cat > /etc/mail/authinfo
     AuthInfo:mail.panix.com "U:cfm@panix.com" "I:cfm@panix.com" "P:*****" "M:PLAIN"
     ^D
 chmod 600 /etc/mail/authinfo
 makemap hash /etc/mail/authinfo < /etc/mail/authinfo

Make sure sendmail has created the proper configuration files.
```
 cd /etc/mail
 make all install
```

Configure relaying. Replace camphor with your machine’s hostname; mail.panix.com with your SMTP relay’s hostname; panix.com with the domain of your e-mail address.

 vim /etc/mail/camphor.mc # before "MAILER" lines, add:
     define(`SMART_HOST',`mail.panix.com')
     define(`RELAY_MAILER_ARGS', `TCP $h 587')
     define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')
     FEATURE(`authinfo',`hash /etc/mail/authinfo')
     MASQUERADE_AS(`panix.com')
     FEATURE(`masquerade_envelope')

If you intend to submit mail while offline, disable sendmail’s DNS checks and configure it to queue mail by default. Replace camphor with your machine’s hostname.

 vim /etc/mail/camphor.mc # after the lines you added in Step 7, add:
     FEATURE(`accept_unresolvable_domains')
     FEATURE(`accept_unqualified_senders')
     FEATURE(`nocanonify')
     define(`confDELIVERY_MODE',`deferred')
     define(`confDIRECT_SUBMISSION_MODIFIERS', `C')
     define(`confTO_QUEUEWARN', `24h')

Build and load the new configuration.

 cd /etc/mail
 make all install restart

Send yourself a test message. Replace cfm@panix.com with your e-mail address.
```
uname -a | mail -s "uname -a" cfm@panix.com
```
If you configured queueing in Step 8, tell sendmail to run its queues manually.
```
sendmail -qf -Ac # clientmqueue
sendmail -qf # mqueue
```

Check the sendmail log.

tail /var/log/maillog

If all has gone well, you’ll see output like this:

May 12 19:31:48 camphor sendmail[87306]: o4CNVmmV087306: from=cfm, size=185, class=0, nrcpts=1, msgid=<201005122331.o4CNVmmV087306@camphor>, relay=cfm@localhost
May 12 19:31:48 camphor sm-mta[87307]: o4CNVmTG087307: from=<cfm@camphor>, size=473, class=0, nrcpts=1, msgid=<201005122331.o4CNVmmV087306@camphor>, proto=ESMTP, daemon=IPv4, relay=localhost [127.0.0.1]
May 12 19:31:48 camphor sendmail[87306]: o4CNVmmV087306: to=cfm@panix.com, ctladdr=cfm (501/501), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30185, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (o4CNVmTG087307 Message accepted for delivery)