Microsoft Exchange NDR messages are delivered to junk folder when using Thunderbird.
Greetings.
My organization experiences a strange issue regarding the Non-Delivery-Report (NDR) messages that are created by Microsoft Exchange Online and this problem occurs only when we use Mozilla Thunderbird and only with my organization's domain (to which i am an admin). When we send an email to a non-existent email address, the NDR generated by Exchange is delivered to junk folder. I have already contacted Microsoft support, but since the problem does not occur when i use their products, they directed me to contact Thunderbird support instead.
No filters or rules have been set within the Thunderbird client. In fact, if i send the message and close Thunderbird before the NDR is received and then open another email client (e.g. Outlook in desktop or online), the NDR is still delivered in my junk folder, so it seems that the filtering is done in the server.
To my best judgement, since the message that is marked as junk is not the one that was generated and sent through Thunderbird but the one that the server informs me that the recipient's address does not exist, it seems to me that it is a server-side problem. Moreover, it seems to me that in this case Microsoft marks its own system-generated messages as junk which sounds a bit strange. However, Microsoft's support directed me to Thunderbird support so here we are.
Any help would be greatly appreciated. Feel free to ask me for any additional information that might be needed.
Thanks in advance.
Wšykne wótegrona (10)
What do you see when you access the account online? If it is a server-side issue, you should see the message in the junk folder.
Yes, i can see the message in the junk folder when using any email client. Every folder in my mailbox is synchronized between Thunderbird, Outlook Desktop, Outlook for android and Outlook Online.
Okay, the info is confusing, as your post implies that the message appears in Junk only when using Thunderbird. I am not sure what support you are seeking.
Ok let me try to clarify then: The "only when using thunderbird" part corresponds to the message i am sending. The message that goes to junk is the system-generated non-delivery report.
So, the message is NOT junk on the server, but is junk in Thunderbird? Have you tried using the Junk filter to mark it not junk? The junk filter needs training on good and bad messages to improve its use.
I believe i have to give some more clarification with examples:
Example 1:
- I start Thunderbird. - I send a new email to some nonexistentaddress@mydomain.com - A non-delivery reply comes back and goes to junk folder
Example 2:
- I start Microsoft outlook. - I send a new email to some nonexistentaddress@mydomain.com - A non-delivery reply comes back and gets delivered in my Inbox.
I understand. The Thunderbird junk filter apparently doing this and needs training to stop doing it. There is more info on this at https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages
No this is not the case. Thunderbird's junk filter is disabled. Furthermore, as i already mentioned in the initial question, if i close Thunderbird before i receive the NDR (so i believe the junk filter did not have time to act) and start another client, NDR is still delivered in junk folder.
If it is relevant, I also used this (following MS support's instructions) https://mha.azurewebsites.net/ to check the headers of two NDR messages. The one that is delivered in my junk folder (in reply to a message i sent using thunderbird) has a total of 125 headers. One of them is X-MS-Exchange-Organization-SCL having the value of 9. The number 9 here means it is SPAM.
The other one, that is delivered in my inbox (in reply to a message i sent using MS outlook) has a total of 54 headers (why this difference anyway?) and the value of X-MS-Exchange-Organization-SCL header is 1 which means it is OK. Those headers have been clearly appended by the exchange server.
I also checked the headers of the messages i sent. The one sent from thunderbird has a few extra headers, one of them being User-Agent: Mozilla Thunderbird. Could it be that MSExchange somehow treats submitted emails differently if they come from a 3rd-party client?
I really have no idea, regarding your question. Further, I don't see where this discussion is going as, for whatever reason, the messages are being flagged. This is a volunteer-supported forum on using Thunderbird, not on nuances of the formatting of various messages that may. I would assist you in documenting a bug, but nothing has shown there to be a bug: this seems more an annoyance. If you determine that there seems to be a bug, you can file it at https://bugzilla.mozilla.org/home
Thanks for your recommendation and for the effort to understand the problem and help me David. As to where this discussion is going, i just hope that someone else has also experienced a similar problem and provides some insights. I do not believe that it is a Thunderbird bug because every test i have conducted points (in my opinion) to the fact that it is a server-side problem. I just followed Microsoft support's recommendation to contact Thunderbird support.
Thanks again for your time and your effort David!