Problem with exim and fetchmail.

I just switched over from sendmail to exim on one of my machines, and
I was having a problem getting mail from any other machine via
fetchmail. If I put fetchmail in verbose mode I can see that exim is
rejecting the SMTP command because there's no domain name:

fetchmail: SMTP> RCPT TO:<rlb>
fetchmail: SMTP< 501 <rlb>: recipient address must contain a domain

But it's fetchmail that's trying to send the mail locally to <rlb>
over the SMTP connection with no domain. I feel sure I've overlooked
something simple. I found that you can fix the problem by using the
fetchmail mda option with a setting of "/usr/sbin/exim -bm %s ", but
the fetchmail FAQ claims this is a bad idea.

$ fetchmail -u rlb -a mailbox.cs.utexas.edu
Enter password for rlb@???:
fetchmail: 4 messages (4 seen) at rlb@???.
reading message 1 of 4 (488 header bytes) fetchmail: SMTP listener doesn't like recipient address `rlb'
fetchmail: can't even send to calling user!
fetchmail: SMTP transaction error while fetching from mailbox.cs.utexas.edu: Unknown error 18446744073709551615
fetchmail: terminated with signal 2

Thanks
--
Rob