[exim] exim4 works but doesn't

I've got Exim 4 running on a Debian Sarge AMD64 build. I've set up Exim per
various howto's and I'm also using Dovecot as a pop3 server. Dovecot works
great, and apparently so does Exim, until I try to send an email from my ISP
account to the mail server I've set up. My DNS records correctly identify
my mail server. My DNS aliases correctly resolve the mail server. When I
send a mail on the mail server to an account on the mail server, it works.
When I test using #exim -bh <ip address> I get a gigantic amount of debug
info that goes WAY over my head. When I try to telnet to the server from a
private LAN system through a NAT server, I can successfully simulate a SMTP
mail delivery session. I can even pop down my hand crafted messages with
the Dovecot popper.



However, whenever I use a different email account to send mail to the mail
server, I receive from my ISP (about a day later) an error mail indicating
SMTP #4.4.1. Has anyone got any suggestions?



Thanks in advance for your help!!