MS is a pain in the rear for every mailprovider. Small mailservers still mostly get through but as soon as you reach a certain thrashold (mails/d) which they dont tell you excact numbers on, they just block you out if they dont consider you a well-known provider. Even if you send mails from hostnames, that live in the domain stated in your RIPE-DB record (which is usually what always gets you delistet instantly)
Their "self-service unblocking" website only works in Internet Explorer, neither Firefox nor Chrome work. And even in IE I always get a random error message even if I follow all steps correctly. So there is now way to get unblocked.
For me, it means that I cannot send emails to my daughters school since they use Office 365 for emails.
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