The recipient address that you are attempting to contact is not valid. Please use the Exchange Admin Center to manage these dynamic distribution groups. Hi Byron, Yes, please change it to verify the result. Issue Description: When external mailboxes send emails to an Exchange Online public folder, an NDR bounced with the error: 550 5.4.1 Recipient address rejected: Access denied. Changing Domain from Authoritative to Internal does disable DBEB See here an article relative to public folders.
It's due to faulty DBEB configuration on Microsoft's side.
In the Look In box, click your primary hard disk (usually drive C), and then click Find Now. Click Start, point to Find, and then click Files or Folders.: 2.
