how to enable ssh of mail users in iRedmail

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

Please help me how to enable ssh of mail user in iredmail.

example:  suppose I created admin user for mail.abc.com  domain then how should I enable ssh for admin
           
ssh admin@mail.abc.com