The reasons are reputation or complaints?
So we got bad reputation on M users and good reputation on Gmail or Yahoo users?
We haven't with a issue with Gmail users so far.
Because we use mail list script, so the script auto unsubscribed the users with these bounced hotmail, msn, live, outlook email addresses.
Our lists have almost zero active M email users now.
But these few remained M users still caused our ip banned few days ago.
We joined the M programs as Smart Network Data Service, junk report or something and excluded the users with complaints from their program. Even though we got < 3 complaints from them a month.
Thinking to disallow M users to register our web service.
Why M owned so many email hostings but their techs are so worse?