Office 365 Exchange Dynamic Distribution Group External Sender Access
How to allow External Senders to submit email to a Dynamic Distribution Group in Office 365 Exchange Online Problem: Office 365 Exchange Online by default will not allow external senders to submit email to a Dynamic Distribution Group, even if the group's Delivery Management is set to allow " Senders inside and outside of my organization ". An example of what the sender will see in the NDR (bounce email) is below: 550 5.4.1 [MySpecialDDG@mydomain.com]: Recipient address rejected: Access denied [BL2NAM02FT035.eop-nam02.prod.protection.outlook.com] Solution: When creating a Dynamic Distribution Group in Exchange on Office365, if you want external senders to be able to send email to the group, you have to adjust the Accepted Domain in the ECP Mail Flow Settings. The domain type must be changed from Authoratative to Internal Relay. Details & Discussion: This is kind of an abnormal use of the Internal Relay setting: Normally you would use Internal Relay i...