squirrelmail - login name and aliases

[nx13464a <nx13464a@net.vodafone.pt>]

Hi all,

The mail server is a Sendmail 8.13.7 and SquirrelMail version is 1.4.6 
and i'm using Debian Sid.
My problem is: a user enter with is user account like user1. When the 
user reply or send a message the information about the sender is 
user1@domain1.com and not the alias name like mike@domain1.com that is 
in /etc/aliases
How can i fix this?

Thanks in advance