Step : 1
- Create a DL & add all users as members (email@example.com), Better this can be Dynamic Distribution Group, Select an option to Include "All Recipient Types"
- Create a Dedicated Mailbox to Catch emails, Which sent to non-existent mail address in Org (Here “Catchall” is Catch all mailbox)
- Set the DomainType to “InternalRelay” (Doing this will make the Rules to take precedence), ECP-> Mailflow -> AcceptedDomains -> Select Domain -> Change the type to InternalRelay
Step : 2
Create a Mailflow Rule as mentioned below:
- If the Sender "Outside the Organization"
- Redirect the message to Catchall@domain.com
- Except if the recipient is member of firstname.lastname@example.org (Distribution Group contains all members)
Note : NDR's won't be generated, Not applicable for Hybrid, Co-Existance, Small business (as no mailflow rules), Not officially supported by Office365 Support.
Refer to : CatchAll-Kingson