Unable to receive emails from gmail

==== Required information ====
- iRedMail version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Web server (Apache or Nginx):
- Linux/BSD distribution name and version:
- Related log if you're reporting an issue:
====

I have successfully installed IRedmail on Ubuntu 14.04, I'm unable to receive emails through gmail. i have disabled greylist but still no progress.

Regards,

Majid Hussain