[Exim] alias@* mail coming through to me

Hi,

I am the local admin for my site, using Exim 4.13, and I've noticed a
strange problem where, if any user sends mail to any domain, but the alias
matches one that's in my /etc/aliases file, then it gets passed through the
aliases file, and eventually ends at me (as I am aliased to root, and
everything is aliased to root).

This obviously creates problems when people try to send mail to
webmaster@??? and it ends up in my inbox (which happened
today)...

Can anyone shed any light on why this is happening and how I can stop it?

Thanks in advance,

Daniel Dainty
s209dan@???