Some hotmail.com users are reporting "subscription was disabled due to Excessive or fatal bounces" errors today. I think we was unable to send to hotmail for some reason for at least some hours.
This sounds DMARC related. Please see https://wikitech.wikimedia.org/wiki/Mailman#DMARC_Compatibility
List administrators may also choose a different DMARC moderation action on a per-list basis by navigating to Privacy options > Sender filters. The possible dmarc moderation actions include: Munge From (default) - Rewrite the From: and Reply-To: Wrap Message - Wrap the message as a message/rfc822 sub-part in a MIME format outer message with From: and Reply-To: as above. Reject - Reject the post Discard - Discard the post
If the issue is still occurring after reviewing/changing the DMARC settings please re-open!