Tambah Port SMTP di ZImbra di centos

  nano /opt/zimbra/postfix/conf/master.cf.in


You will see  config line bellow
smtp      inet  n       -       n       -       -       smtpd


Under that line, add the following config.

 587      inet  n       -       n       -       -       smtpd

Done, now you can setup your mail client to use your Zimbra server with that custom 587 port instead of the standard 25. The standard 25 port will still be accessible, so technically you can use either.

 Then, restart the MTA:

# su - zimbra
# zmmtactl stop
# zmmtactl start

Copy From  

1. evilangelist.com
2. http://wiki.zimbra.com