My reseller created new acc for his client then....

My reseller created new acc for his client then.... his clients tries to setup additional ftp account (virtual ftp)

His clients can't loging to those additional ftp that he had created using username / pass but he has to use username@domain.com / pass then he can login

Same for the emails as well.

Any idea why is that?
Can i change it so user can login to their email and ftp by just using username/pass instead of username@domian.com / pass

Thank You.