Configuring sendmail behind a firewall

define(`SMART_HOST',`mailrelay.example.com')dnl

# m4 /etc/mail/sendmail.mc > /etc/sendmail.cf

# /etc/init.d/sendmail restart

host map: lookup (mydomain.com): deferred)

define(`confSERVICE_SWITCH_FILE',`/etc/mail/service.switch')dnl

# cat /etc/mail/service.switch
  hosts files

DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')

DAEMON_OPTIONS(`Port=125,Addr=127.0.0.1, Name=MTA')

DAEMON=no

DS

DSmailrelay.example.com