[Exim] server name with virtual hosts

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Hi all, and apologies in advance from a newbie, but have been going in circles for days, and searched the archives till the brain no longer thinks straight, if it ever did.
Have a server, apache, running virtual hosts, with cpanel and frontpage extensions amongst other things.
From any fill in forms on any of the domains hosted, the FROM address in the resulting email is
username@servername
How do I get it to show
username@???
The problem is that many pre made scripting utilities like frontpage, obviously use hostname I am guessing, but I thought this should automaticly resolve to the domain that the script or form is located on.
The reply address is ok, it is just the from address, which is unsightly and very unprofessional looking. Custom scripts are no problem at all as we can control them but many of our users use frontpage.
Any suggestions would be very welcome, surely someone out there has had a problem like this before and found a fix for it?
Regards
Gregg
tlc@???
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