sending mail outside local domain

[John Steniger]

I've recently set up qmail 1.03 on an OpenBSD 2.6 system.  I can send and
receive e-mail locally, but when sending out to the internet I get the
following error:

Connected to 198.23.2.45 but sender was rejected.
Remote host said: 501 <<[EMAIL PROTECTED]>> ... Sender domain must
exist

I have no MX record for tester, as it isn't the default mail server for the
domain (using it for testing).  
Any idea how to fix this?  Would a second MX record at lower priority do?

Thanks