Why are there two entries in the Microsoft 365 message trace for emails with a signature applied?

Query?

When you perform a message trace in Microsoft 365, you notice a duplicate entry for all email messages with a signature.

Answer

This is expected behaviour when using Exclaimer.

The Microsoft 365 Tracing tool displays an entry for the email message that is being routed from your tenancy to the Exclaimer-hosted servers.

The duplicate entry is for the email message returned from Exclaimer to the Microsoft 365 tenancy, for delivery.