Outgoing mail being sent as expanded distribution lists and filtered by office365 as spam
Hello all,
Trying to solve a significant outgoing email problem here - that appears to have started around January 24th (around the time of the latest Thunderbird release - but possibly before.
Outgoing mail from my organization is being filtered as spam by Office 365 outgoing mail servers (or being sent through high risk servers and being filtered by the recipients black list service (such as Barracuda) because it is coming through said out going mail server.
Our IT support has suggested that it is being caused by out going messages being sent as "expanded" or "expanded distribution lists" even when only sent to one person (via to:).
This issue has been effecting our entire office for close to 2 weeks, but has been difficult to pin down as we only received our first two Undeliverable return receipts yesterday afternoon (that highlighted the Barracuda black list problem). Our IT support was simultaneously looking into it on the office 365 back-end and discovered the messages being tagged as "expanded" and then filtered into spam.
We are all Mac based, running Thunderbird, generally on OSX 10.11.6
Any and all suggestions are welcome!
All Replies (4)
Update:
The expanded distribution symptom may be a red herring.
We have removed that from the equation by disabling an automatic notification system for emails that were identified as spam to be forwarded to our IT specialist. Message traces via Office 365 no longer report the blocked messages as being "expanded".
Outgoing emails from Thunderbird on a Mac, up to and including plain text emails that just say "test" are being filtered out as spam by Office 365 Servers.
Emails sent from the windows version of Thunderbird work fine, as do "office" emails sent through a personal email account such as google (aka circumventing Office 365 servers).
We have also tested future (beta releases of Thunderbird) as well as previous releases (52.5.0) of Thunderbird that were working normally before the issue started (EDIT: Jan 19th). All such emails are being blocked since then.
Modified by sjNumberTen
All such emails are being blocked.
So this isn't a Thunderbird problem. Work with your IT support and email provider to address the server issue.
That is where we sit right now.
As far as I am concerned we have eliminated Thunderbird as the 'primary' cause.
5 users are unaffected (4 of them are low-traffic users) 1 user has only had 2 of their emails affected (out of hundreds), seemingly at random. Rest of the users are being severely impacted (10-11 users). Windows version of Thunderbird works without issue.
So far - as of Friday afternoon - IT support as well as Microsoft's stance is "You're using an unsupported email client - it's not our problem, use outlook and everything is fine".
(Which IMHO, is an unacceptable response.)
Modified by sjNumberTen
Based on my current tests the issue may have "inexplicably resolved itself".
24 days later.
I am not longer seeing outgoing spam flags on messages sent to my personal accounts and several others I have tested.
Hopefully this is the case. And if something was wrong in the office365 cloud that it was resolved, even if they told us it wasn't their problem.