[CentOS] Postfix login Name Error

Dear Friends,

I have done basic postfix mail server configuration but problem is when I try to login then it is not taking my name . it is taking full name with domain name. My domain name is *"studen.ac.in"* My user name is jiten when I try to login with my name in a log it is showing *" Sep 5 10:06:56 neu dovecot: imap-login: Aborted login (auth failed, 1 attempts): user=jiten@ac.in, method=PLAIN, rip=192.168.1.2, lip=10.112.1.2, secured "*

But when I try to login with* jiten@student.ac.in *it is working fine . So please help me how can I remove or hide my domain name when I and other user want to access my mail server .