I'm trying to configure sendmail on our Debian Linux server to send mail, using our Exchange server as a relay. I'm a total noob at all of this. We can send mails to internal addresses (for example, if our domain name is ourdomain.com, the server can send mail to firstname.lastname@example.org) with no problem. We can't send mail to external addresses like email@example.com or firstname.lastname@example.org. Here's an example of what I get in /var/log/mail.log Mar 7 14:45:29 newton sm-mta: r27JjOw1017159: to=<email@example.com>, ctladdr=<firstname.lastname@example.org> (0/0), delay=00:00:05, xdelay=00:00:05, mailer=relay, pri=30455, relay=webmail.ourdomain.ws. [xxx.xxx.xxx.xxx], dsn=5.7.1, stat=User unknown Also, I get this: Code: root@newton:/etc/mail# sendmail -bv email@example.com firstname.lastname@example.org... deliverable: mailer relay, host webmail.ourdomain.ws, user email@example.com Does that mean the firstname.lastname@example.org is unknown to newton, or unknown to Exchange? Is there something in Exchange we need to configure? I have no idea what to configure. Please help. Thanks!