sendmail problem
 

i have sendmail 8.13.8 running on my solaris 10 .
i have installed qpopper as my pop3 server daemon
i have updated my sendmail.cf and submit.cf
i tested if sendmail was running correctly with:
telnet "localhost" 25
i get an OK on that.
i also did :
telnet "localhost" 110
and qpopper is running fine also.

i use Outlook Express as mail client
i setup my user account normally.
now this is where my problems begin
when i try to send a message i get this error from outlook:

The message could not be sent because the server rejected the sender's e-mail address. The sender's e-mail address was 'jdandre@brh.net'. Subject 'test', Account: '172.16.7.42', Server: '172.16.7.42', Protocol: SMTP, Server Response: '451 4.3.0 Temporary system failure. Please try again later.', Port: 25, Secure(SSL): No, Server Error: 451, Error Number: 0x800CCC78

is there anything missing ?
hope u guys can help me
thnx in advance

Dody