We currently have a server set up as an email sending box. It has a Windows Service setup to periodically send emails through an SMTP server which is configured on the same box. The service and SMTP server are generally working fine, as I can send emails out to most addresses, and receive them okay.
The only scenario which it isn't working for - and that is to our Exchange email addresses. The email sends okay, and according to the log, it get seems to get relayed to the server okay (see output below) - but no one receives the email.
We're not using a from address that matches a user or domain on the Exchange server, as my initial thought was that it would get rejected due to not being authenticated. Even just using firstname.lastname@example.org fails.
It's also not going into the Junk Mail folder (unless there could be some sort of higher level filtering going on).
Sadly we're developers here, so knowledge of Exchange is fairly limited. But is there anything obvious which would cause this? My concern is that we'll have the same issue when mail is relayed to other (Exchange/email) servers.