[Exim] alias question

Hi all,

I have discovered a hole in my Exim setup.

I have users aaa, bbb, ccc on my server.

and alias files of

domain - which contents of the file are

*.somedomain.com: somedomain.com

and the contents in the file somedomain.com

user-x aaa
user-y bbb
user-z ccc


ie....if i mail user-x@???, mail delivers to user aaa ...so on so
forth.

the problem is if i try to email to aaa@???, that gets delivered
to user aaa as well.

how do i stop that ?

thanks in advance for you help.

regards

chris g