Using exim4 and fetchmail with imap and authenticated smtp

[Tom Badran <tb100@doc.ic.ac.uk>]

Im using exim4 and fetchmail to recieve email from an imap server using
tls, and send using authenticated smtp on an smtp host at the same site.
However, when i look over the headers of emails i send, i see lots of
them contain tom@locahost which is my local username, rather than the
email address of tb100@doc.ic.ac.uk

Is this normal and am i being paranoid? I set up all the packages making
as little modification as possible to what debconf produced. I made a
few changes to get authenticated smtp working, and did my fetchmail by
hand and it all seems to work, i just worry about things ;)

Thanks

Tom