FALSE Mailer-Daemon "Undeliverable" responses to Confluence automatic Notifications

[Rodney Hughes]

Any help appreciated ... question at the end

We run Confluence Server 8.5.5 for a global community with over 8000 Users.  Of course every day we send hundreds of activity Notifications in our Groups and bunches of "Recommended for ...: 

But every week we get DOZENS of Mailer-Daemon responses as "Undeliverable"
Sometimes the details say "Host or domain name not found" or some other comment.

I used to think the alert was true ... but turns out most often it isn't!

A few Users of course have changed companies so their emails"bounce" and we get a "User does not exist" notification from their old company email host so we act on those to try to get a new email for the User.

But for other M-D responses and having contacted the intended recipient myself using the address originally used in the Notifications ... 
Turns out sometimes the "Undeliverable" response is FALSE because the User replied to me .. so clearly we are using correct and valid email addresses

More intriguingly ... in a couple of cases I queried, the User told me they DID receive the email whilst others confirmed nothing received

so the "Undeliverable" response is clearly FALSE in some cases

Now here is the extra strange thing .. with a global User base, 99% of these Undeliverable responses are specifically related to Users in Russia .. both company domains as well as  private email domains like yandex.ru and mail.ru etc 

So I contacted their domain hosts
ALL have replied that there is nothing at their end configured to actually block our emails or trigger a false "Undeliverable" response.

So something in the internet between our host machine and theirs somehow triggers this false response!   
so I don't know when or when not to trust the M-D response as something we have to fix
:(

Even more intriguingly, I was told in this last week that Atlassian Russia had closed down a while back .. but I dismissed that as not having relevance ..
until I spotted one of the Details attachments in the Undeliverable response which says at the bottom (the *** are actually numbers):

MIME-Version: 1.0
Content-Type: multipart/related;
boundary="----=_Part_2160_***********"
X-ATLASSIAN-NOTIFICATIONS-VERSION: 18.5.21
Auto-Submitted: auto-generated
Precedence: bulk

SO .. finally to the question for this Community

Does anyone know how to "fix the internet" to not issue false "Undeliverable responses to our Confluence generated emails?

[Ash Yadav]

Hmmm.. this is interesting. 

I've not personally encountered this however I'd say this is probably a bit outside the scope of the general community forums to accurately triage. 

A quick google search returns similar results from users reporting a similar problem with other applications and does not seem to be specific to just Confluence behaviour. This leads me to believe that this is more network related than Confluence itself. 

Without access to logs and some testing, this would be difficult to pin-point. 

I'd personally start with getting on a session with Atlassian Support and analysing the logs if you haven't already done so and see if you can further narrow it down. 

KR, 

Ash