Dovecot configuration for Users to use only 'username' as login and default domainname to be added

Can anyone help me to find urgently solution (if exists)?
I have migrated users from old imap server to ISPConfig/Dovecot
Now users need to change configurations in all Mail clients to use 'username@domain' as loginname, instead of 'username' for old imap server.
Since I have only one domain used for ISPConfig now. I wonder if I could find a way to configure Dovecot somehow to continue accept 'username' as loginname during 'imap-login', but to add my deafult '@domain' part for proper auth process to be done via ISPConfig.
I understand that this is dovecot-config related, but would be very thankful if someone help me.

 

I have found the solution,
Just needed to add the following option in dovecot.conf:
auth_default_realm = <yourdomain>
and it adds that domain in case users don't supply '@domain' part as username.