Relevant products: Exclaimer Cloud - Signatures for Office 365
Emails sent from an internal user to another internal user are not routed to Exclaimer Cloud
Undeliverable journal reports are being sent to an internal mailbox:
The Microsoft Knowledge Base article below provides a solution for this problem:
In short, a dedicated mailbox must be specified as the recipient for Journal Report NDR messages. This is achieved using the command below:
Here, the <email@example.com> placeholder represents the email address of the user.
Microsoft recommends that the JournalingReportNdrTo recipient is set to an external email address, or that a dedicated mailbox is created, which has no transport or mailbox rules applied.
This solution applies even if message journaling is not enabled.