[Exim] Accounts and Domains

Hi!

I have a setup here wich surely is not quite optimal.

We host some Domains on a machine. All user accounts are standard unix
accounts. Direct login is not possible. To avoid conflicts with two people
having the same last name i build accounts like [first letter of first
name][last name]. So my name is Daniel Buchholz, my account is 'dbuchholz'.

We then have mail adresses like [last name]@domain which is buchholz@ in my
case so we have several aliasfile directors to have this done.

But the problem is:
- Mail directly to acount names is possible (which is not critica I think?)
- Mail to [accountname]@[some other hosted domain for which this local part
should not work] and that I definitely don´t want to see.

Any ideas?

Daniel