[exim] Email address getting primary host appended.

Can someone point me where to have Exim not append the primary hostname to
email addresses? This is written to the log:

2011-10-26 00:45:38 1RIrcg-0003a0-Fg "duane@???" from env-from
rewritten as ""duane@???" by submission mode

The primary host name is hp.fbsd. It is a FreeBSD guest OS within
VirtualBox running on Ubuntu 11.04.

hp.fbsd is resolvable locally as:

hp# host hp.fbsd
hp.fbsd has address 192.168.2.84
hp.fbsd mail is handled by 10 hp.fbsd.

Likewise, dubuque.org is also resolvable:

hp# host dubuque.org
dubuque.org has address 192.168.2.84

-duihi77