I am a noob to Linux. We have Debian 7.4 with exim4. I'm trying to configure it to use our office365 as a relay, but I have no idea what to do. This is what the logs show when I send a test message (some parts have been changed to generic terms for security): Code: 2014-04-17 08:51:56 1WalnI-0006xO-Uc <= [email protected] U=test P=test S=325 2014-04-17 08:52:01 1WalnI-0006xO-Uc TLS error on connection to <ip address> [<ip address>] (recv): A TLS packet with unexpected length was received. 2014-04-17 08:52:01 1WalnI-0006xO-Uc TLS error on connection to <ip address> [<ip address>] (send): The specified session has been invalidated for some reason. 2014-04-17 08:52:01 1WalnI-0006xO-Uc ** [email protected] R=smarthost T=remote_smtp_smarthost: SMTP error from remote mail server after MAIL FROM:<[email protected]> SIZE=1360: host <ip address> [<ip address>]: 530 5.7.1 Client was not authenticated 2014-04-17 08:52:02 1WalnO-0006xU-0K <= <> R=1WalnI-0006xO-Uc U=Debian-exim P=local S=1223 2014-04-17 08:52:02 1WalnI-0006xO-Uc Completed It looks like exim4 needs to authenticate, but I don't know how to do that. Please help, thanks!