Hi all,
Microsoft's mail services are a tough party to work with. While GMail uses a moving average system to block mail (in the sense that they never *completely* shut down a sender, but monitor the quality of the mail stream coming from it, even if it's 99.9% shut down, Microsoft will simply kill off the entire mailflow, disabling the possibility of automatic rehabilitation.
Today I had to ask Microsoft to delist us (this unfortunately happened before, so I could say "again"); the reason is that we have a relatively large number of moderators subscribed to Microsoft sevices.
Why is this a problem? Well, Mailman will stubbornly try to deliver moderation reminders, even if the reminders have been rejected by the MS mailserver for suspect virusses. With very few actual subscribers on MS infrastructure, these reminders constitute a high percentage of our mail flow to e.g.
outlook.com.