User has Word 2002 SP3 and GroupWise email

His data comes from a 3rd party program which produces a tab delimited file.
I have examined the data and find nothing irregular.  When he merges his
document directly to email, the majority of his mailmerge list of addresses
have no To: listed either in the email Inbox or when the individual email is
opened.  When we merge this same data file to documents instead of to email,
the addresses populate correctly in the document.  Can anyone give me a clue
as to what to look for in this problem?  It is doubly difficult because to
test involves actually sending out junk email, which the user does not want
to do.

Thanks much for any help offered.