Setup CatchAll-Mailbox for specific domain in Exchange

New Contributor


I want to introduce a CatchAll-Mailbox, meaning that all messages sent to non-existant recipients shall be redirected to a specific Mailbox.


The basic idea is to introduce a rule that redirects all incoming messages and make an exception for recipients who are member of a Dynamic Group that contains all existing Mailboxes. To prevent exchange from instantly blocking the message and instead process the rules, i set the Accepted Domain to internal relay. 


Now i want to make this whole thing domain-specific, meaning it should only apply for unknown recipients of I tried to introduce a recipient-matches-pattern-condition but that didnt work. 

How can i set this up?



4 Replies
There's a "domain is" condition, try that? Or is this for on-premises Exchange?

@Vasil Michev Yeah there is. I also tried it but it doesnt seem to work.

My rule does the following:


If sender is outside organisation...

...redirect to

..except if recipient is member of dynamic group (Group contains all existant Mailboxes


This works for sending a mail to


Now if i introduce a second condition like:

... and if recipient's domain is ''...

the rule never triggers. I assumed that maybe the domain condition only works for users that actually exist, but i also couldn't get it to work with other condition types. Maybe i used it wrong?


Can you try with removing the dynamic group condition?

@Vasil Michev doesn't change it, the rule just won't trigger. Keeping the Dynamic group and removing the domain condition instead results in a working rule.


Looking in Message Trace i can see that Exchange just let's the mail through. Because the domain is set to internal relay it just tries to redirect the mail to the original recipient, resulting in a loop recognition that blocks on third redirect.