Sendmail

Routing all outgoing mails via the outgoing smarthost:

  1. Ensure the IP address is added as an authorized smarthost (without authentication)
  2. Ensure the outgoing user has correct limits set matching your traffic volumes
  3. Update your configuration:
    1. For this you have to edit /etc/sendmail.mc and add the following lines at the top under the "pert(-1)dnl" line:

      2. define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl
      define(`SMART_HOST', `[SMART.HOST.TLD]')dnl

    2. Run "sendmailconfig" to use this new configuration

      3. This will automatically re-start sendmail

Alternative Configuration with username authentication (un-tested)

  1. Change directory to where your sendmail configuration files (sendmail.mc and sendmail.cf) are located, usually /etc/mail/
  2. Create a safe sub-directory (suggested name auth/):
    3. # mkdir auth
# chmod 700 auth
  3. Create a file with your authentication information (suggested filename: auth/client-info)
    4. AuthInfo:SMARTHOST: "U:USERNAME" "P:PASSWORD"
  4. Generate the authentication database and make both files readable only by root:
    5. # cd auth
# makemap hash client-info < client-info
# chmod 600 client-info*
# cd ..
  5. Add the following lines to your sendmail.mc file
    6. define(`SMART_HOST',`[SMARTHOST]')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 587')
define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
FEATURE(`authinfo',`hash /etc/mail/auth/client-info')dnl
  6. Generate sendmail.cf
    7. # m4 sendmail.mc > sendmail.cf
  7. Restart the sendmail daemon
    8. # kill -HUP `cat /var/run/sendmail.pid` (old-school) -OR-
# make restart (FreeBSD) -OR-
# /etc/init.d/sendmail reload (debian Linux)
  8. SMARTHOST should be replaced with your SMTP hostname