I had use cases where mailboxes in 365 had to be configured to automatically forward emails to an external system. This could be a CRM or Ticketing system.
However you'll find out very quickly that 365 doesn't apply many checks on the emails at all when you configure the forward.
Configuring a forward either through a Transport Rule or directly on the mailbox itself as an administrator doesn't seem to trigger the 365 spamfilter or any other filters at all.
You can test this by triggering the spamfilter in 365 by sending a mail with this in the body:
XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34X
If you check the message trace, you will see that it gets marked as spam, but 365 will still forward it to the external mailbox.
The only way to resolve this issue and having the emails checked before they are forwarded is by either
- Have the mailbox integrated with the CRM or Ticketing System.
- Configure a Mailbox rule in the mailbox itself, login to the mailbox through OWA and configure the rules there
The emails will then land in the mailbox first, thus triggering all filters and then forwarded.