[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 at ac.in>, method=PLAIN, rip=192.168.1.2,
lip=10.112.1.2, secured "*

But when I try to login with* jiten at 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 .

-- 
Thanks & Regards
Jitendra Jha
+91-7498370550