Zimbra Mail Server
 

A few days ago, I was having issues sending mail to external domains while using mobiles devices.While trying to resolve the problem, I came across and decided to implement Now I need to reverse the above because none of my mails are going to other domains!!!!
Any help will be highly appreciated.

I've managed to solve the problem albeit temporarily by editing main.cf . It seems to work until I restart the service

If you just want to reverse what you have done you should be able to run:
This would permanently clear the value you had set. The main.cf Postfix file gets recreated each time the Zimbra services start up.

If you continue to have issues you might want to consider posting on the Zimbra forums. They are very active and have a lot of very knowledgeable users.