Connection Timed Out to some domain

==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.8.7
- Linux/BSD distribution name and version: Ubuntu 12.04.3 LTS 64-bit
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):  LDAP
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro?
- Related log if you're reporting an issue:
392D72300089  1140269 Wed Jul 22 10:02:49  xxxxx@xxxxx
   (connect to xxxxx[xxx.xxx.xxx.xxx]:25: Connection timed out)
                                         xxxxx@xxxxxx
====

Is there some way to add a relay if my redmail is not being able to send to other domains? We experience this to few domains only

Thanks