[exim] making FROM: field a specific user

I need help making exim4 set the  FROM: field to a specific user

I really have RTFM ... I obviously don't understand what I read. I am trying
to get exim4 to send all mail from bugzilla at virtualinstruments.com (with
the at the thing over the 2 which I didn't use so this email program would
not code it as an email address)
Instead it sends it from www-data at virtualinstruments.com
if I do an ls -l in the bugzilla directory the owner shows as www-data
that is what bugzilla did when it installed itself from binary because I
spent four days and could not get the source to install.
[note: we will not go into the three weeks I beat my head into a wall to get
decode::detect to install so I could import the old bugzilla data base (one
must install g++ but no one or nothing tells one that - I finally googled
each and every error line and finally found one had something to do with c++]
okay so now all I want to do is communicate with exim4 that no matter what or
whom passes it email to send, it is to put bugzilla at virtaulinstruments.com
in the from: in the headers.
I have tried everything in the docs that appeared to relate as in
untrusted_set_sender = *
???
do I sent that to
untrusted_set_sender = bugzilla at at virtualinstruments.com
or
I'm getting to think windows might have a good side and that is scary
thanks
gayle
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