squirrelmail virtual users

[pvc]

hi another question bout mail..

i just installen squirrelmail and it works like a charm,
that is it works good for "true"users from my primary domain.

the problem is i want to use squirrelmail specially for "virtual users
ie users at the secondary domain with no shell acces.

like
in /etc/postfix/virtual:
user1@virtualdomain.com user1

but user1 has no shell acces,

if i try to log into squirrelmail with one of these ttype users i get a wrong username or password error, now i dont know wether the problem lies with the fack that user1@virtualdomain is a mapped alias and thus squirrelmail cant find it, or that it got something to do with the fack that the user has no shell account.

anyone have any idea how i can solve this?

thanks in advance/