Monit: Postfix

postfix

# Postfix
check process postfix with pidfile /var/spool/postfix/pid/master.pid
   group mail
   start program = "/etc/init.d/postfix start"
   stop  program = "/etc/init.d/postfix stop"
    if failed host YOUR-RELAY-HOST port 587 
      type tcp protocol smtp using tls
       with timeout 15 seconds
      then alert
    if 3 restarts within 5 cycles then timeout
   depends on postfix_rc
   depend postdrop_bin
   depend postqueue_bin
   depend master_cf
   depend main_cf
   
   check file postfix_rc with path /etc/init.d/postfix
   group mail
   if failed checksum then unmonitor
   if failed permission 755 then unmonitor
   if failed uid root then unmonitor
   if failed gid root then unmonitor

 check file postdrop_bin with path /usr/sbin/postdrop
   group mail
   if failed checksum        then unmonitor
   if failed permission 2555 then unmonitor
   if failed uid root        then unmonitor
   if failed gid postdrop    then unmonitor

 check file postqueue_bin with path /usr/sbin/postqueue
   group mail
   if failed checksum        then unmonitor
   if failed permission 2555 then unmonitor
   if failed uid root        then unmonitor
   if failed gid postdrop    then unmonitor

 check file master_cf with path /etc/postfix/master.cf
   group mail
   include /etc/monit/templates/rootrc

 check file main_cf with path /etc/postfix/main.cf
   group postfix
   include /etc/monit/templates/rootrc

YOUR-RELAY-HOST is that service who will deliver emails of a server, like Amazon SES, Gmail or Mailgun.