[Hampshire] Sendmail local users

Hi,

I'm having real difficulty getting Sendmail to accept mail for local users.

I use fetchmail to collect mail from my ISPs POP3 service and that
presents the mail to sendmail as <username>@localhost. All is well as
the mail is accepted and shunted off to procmail. I use the ISPs tools
to set aliases and suchlike on their system so it all ends up in the
correct POP3 boxes. No problem there.

However, when a local user (for instance, my brother) wants to send me
an email he addresses it as first.lastname@??? and then his mail
client connects to port 25. Sendmail rejects this as first.lastname is
an "Unknown User".

Which part of sendmail is it that can translate first.lastname into
username, and how can I turn that feature on?

I've already tried the following:
virtusertable (including the makemap hash virtusertable.db <
virtusertable part).
any domain works as long as it's listed in /etc/mail/local-host-names
and the user part is a local username.

This only affects local users, and I can work around it by sending the
mail through my ISPs outbound server, but that is a waste of bandwidth
having the mail go up the wire, only to come back again 2 minutes later!

Any help appreciated, even if it's a step-by-step guide to using another
mail server.

--
Graeme Hilton