[Migrated from MSDN Exchange Dev] O365 public folder has contributor permission for "anonymous" but still rejects external email

Question

[Note] This thread was originally posted on MSDN. As the MSDN Exchange Dev forum mainly focuses on developing issues and the TechNet Exchange forums for general questions have been locked down, we manually migrated this one to Microsoft Q&A platform to continue the troubleshooting.

[MSDN thread link] O365 public folder has contributor permission for "anonymous" but still rejects external email

Answer 1

Hi,

For the issue you are experiencing, it may be resulted by inappropriate accepted domain type. When the accepted domain is set to Authoritative, Directory Based Edge Blocking (DBEB) allows any SMTP address that has been added to the service, except for mail-enabled public folders.

To solve this problem, change the accepted doamin type to "Internal Relay". You can follow the steps below to perform a quick change:

1. Go to Exchange admin centerand sign in using your credentials.
2. Choose mail flow > accepted domain mains, and doble click the target domain.
3. In the pop-up window, change the accepted domain to "Internal relay".
4. Save your changed.

For detailed information and instructions about accepted domains: Manage accepted domains in Exchange Online

Here is also a thread discusses about the similar issue as yours: Public folder was given Anonymous user "CreateItems" permission, Still cannot send that public folder emails from the outside world

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