How to add an aditional smtp port

==== Required information ====
- iRedMail version: iRedMail-0.8.5 has been released.
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LADP
- Linux/BSD distribution name and version: ubuntu 14.02
- Related log if you're reporting an issue:
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Hello, I am writing because I need to add an additional port for SMTP
Currently everything works on port 25, but some users have problems with that port, so it would add an additional port (925).
How do I add that port and that works for the 2 ports simultaneously.
I hope you can help me.
regards

Gonzalo