Username with no domain for login

==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.8.7
- Linux/BSD distribution name and version: Centos 6
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): Apache
- Manage mail accounts with iRedAdmin-Pro? Yes
- Related log if you're reporting an issue:
====
Hi,

I need to let users for one domain to identify them selves only with the username part of the email address (all ways, SMTP, POP, IMAP and Webmail)

I now Roundcube provides a way to setup it, but I don't see how to for the rest of the protocols.

Is it possible?
Any clue will be truly appreciated.

Thanks you so much,
Jorge.