[Mailman-Users] Many users unsubscribed at once (not by me)

[Bill Cole]

On 13 Dec 2015, at 13:56, Mark Sapiro wrote:

> In fact, the fact that almost all the unsubscribed users were hotmail
> makes it seem that this is not DMARC, but more likely hotmail
> (Microsoft) blocking the sending IP.

And with the one other being live.com.au (roughly: Australian Hotmail) 
it becomes a distinctively Microsoft problem.

For what it is worth, recently the policy staff and policies of 
Microsoft's former-Hotmail and former-Frontbridge have seemed to be 
converging/merging. One win for the world of this is that the chronic 
problem of Hotmail/Live.com mail being accepted but silently discarded 
has been replaced by overt rejection at the MX border (no, not THAT MX 
border) in many cases. For Mailman lists, one result is that long-dead 
addresses are getting cleaned out because they are now bouncing. Another 
result is that some silent discards have been replaced by delivery, so 
in some cases people who haven't seen mail from a list in years and now 
are seeing it and telling MS that it's spam. The second process can lead 
to broad blocking across MS-hosted domains, but at least now it is 
visible.