Office 365 plan E3. One public folder, enabled email and it works when users from the same domain sends mail. Have set the anonymous to have write items. When external users sends mail this is the response.
The message was rejected by the recipient's domain because the recipient's email address is not listed in the domain directory. You may e-mail address is misspelled or does not exist. Try to solve the problem by doing one or more of the following:
1.Send message again, but delete and enter the address again before sending the message. If your email program automatically suggests a link you can use, do not choose it. Enter the full email address.
2.Empty list for autocompletion of recipients in e-mail program by following the steps in this article. Then send the message again.
For email administrators
Directory Based Edge Blocking (DBEB) is activated for the recipient's organization, and the receiver was not found in the directory. If the sender is using the correct address, but the problem still exists, contact the recipient's e-mail administrator and tell him or her problem. The problem can be solved by synchronizing the local directory and directory in the cloud again.
Remote Server returned '550 5.4.1 [xxxxxxxxxxxxxxxxx]: Recipient address rejected: Access denied'
I'll try to get an answer from Microsoft if this is the expected behavior, but that will probably take some time due to the holidays.