Got a strange case today, a user was complaining about her cannot receive emails from a distribution list where supposed a mailbox was sent multiple emails but nothing comes in her Inbox. In this post I’ll demonstrate the troubleshooting process along with the resolution.
The troubleshooting process
When I checked with the user to understand the issue, I immediately run some checks with both the distribution list and the mailbox via Exchange admin center. Then I found out that: distribution list A – is a recently created distribution list for specific group of users, and the mailbox B – is a user mailbox that was created for sending automated email by some application.
After understood both distribution list A with mailbox B, Heading to “Mail flow” > “Message trace” > select “Start a trace” > enter the mailbox B in the “Senders” > enter distribution list A in “Recipients” > click “Search” within Exchange admin center.
Great! There are four failed reports being found in Exchange admin center. So, select the first one to checking the latest report > after review the report confirmed that the message was not delivered.
Checking closely under the “Message events” > it shows the reason with key words “SenderNotAuthenticatedForGroup; Authentication required; Delivery restriction check failed because the sender was not authenticated when sending to this group”. Exactly, that’s the root cause of this issue. Furthermore, under the “Message ID” can see that this message was sent from a legitimate SMTP server with the IPv4 address.
Given the fact that the mailbox B’s email was not delivered due to “an authentication issue”, so the next focus point should be examining the distribution list A. Heading back to Exchange admin center > “Recipients” > “Groups” > “Distribution list” > search that distribution list A > select to checking more details > select “Settings” > select “Delivery management” > gotcha – under the “Sender options” it was been set to “Only allow messages from people insider my organization”.
Then I change the option to “Allow message from people insider and outside my organization” > click “Save changes” to apply.
Revert back to the user to let someone who possessed access to the mailbox B to sending some test email to that distribution list A > received successfully!
Conclusion
For such an issue the first thing to do is always to knowing the object you’re dealing with. Then once you’ve known the object you can dig deer with Exchange admin center. Lastly, remember regarding email delivery issue always using the “Message trace” feature in Exchange admin center to trace the message from sender A to recipient B. Then examine the report for further detailed clues.
