We are running an Exchange Hybrid solution between Exchange Online and Exchange Server 2019. We need to figure out a way to monitor if someone tries to send mails to one of a select few highly critical mailboxes where it was not delivered for whatever reason. My initial thought was to create a transport rule, search for the postmaster sender and do a regular expression match for the e-mail addresses. This was not possible. I then tried various variations where I searched for "Undeliverable " in the subject line and similar. This does not work either. I then found out that because it is a system message transport rules does not apply.
I then figured maybe you could create an alerting policy in Exchange Online, but apparently these are also quite limited.
I'm now down to have to use a powershell script to look at the mail flow and then send a mail based on this. But I really prefere something I can implement through the graphical interface.
Does anyone know of a way to let our supporters know if delivery of a mail to a select mailbox have failed? Preferably without powershell.
Thank you! :-)

