Relevant products: Exclaimer Cloud - Signatures for Office 365
Emails sent from an internal user to another internal user are not routed to Exclaimer Cloud and 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 journalling is not used.