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.