[exim] Virtual domains and local user accounts

Hi all,

I am running Exim version 3.35 on a Debian (stable) server.

When an email arrives for an address at one of the (several) domains
hosted on this box, I often want to deliver it to a local user
account. I have a virtual domain director set up and a set of alias
files, one for each domain.

The problem I have is this: Suppose that one of the lines in the alias
file for somedomain.com looks like this:

webmaster : fred

...the intention being that email addressed to
'webmaster@???' is for local user 'fred'. Unfortunately,
trouble then ensues, because Exim seems to think this means
'fred@???' and rewrites it accordingly. If the file also
contains the line:

fred : privatefred

...the result is that Exim re-aliases the message and mail for
'webmaster@???' actually goes to 'privatefred'.

This behaviour maybe makes a vague kind of sense for single domain
systems, but is obviously completely crazy for multiple domain systems
where it isn't possible for fred@??? and fred@??? to
both correspond to an account of the same name.

So... please could someone recommend a solution or workaround for this
? If fred@??? and fred@??? both want accounts so that
they can run Exim filters from their .forward files, how do I deliver
their mail ?

Cheers,

Dom.