> MS seems to have difficulty getting its servers into the DNS, and does not seem to care that the SMTP RFC requires that machines sending email are in the DNS.
Not malicious, just incompetent. Incompetent, incompetent, incompetent!
As msobkow says, MicroSoft has never taken email -or- DNS seriously. (Not invented here?)
Back in the 2006 era, my university started enforcing DNS back-match on incoming email, and about 5% of MS-box emails were being rejected. Users thought _I_ was blocking them! (I didn't even touch the servers, just desktop support.)
This was in a spam epidemic (we didn't yet know how bad spam would get) so blocking un-DNS IPs was a very valid thing to do, to take load off our tightly funded mail server.
Over several weeks, the university postmaster and I documented a large block of MS IPs that were sending email but not registered in DNS.
My impression was that MS was replacing about 5% of their email machines every month, but NOT putting the replacements on the old IP (one logical process). When someone eventually noticed that only 99% of emails went through (maybe 1 in 5 destinations were checking IP/DNS) they appointed a geek to try to figure it out. And frequently they fixed the ONE machine the geek had found, and ignored the larger problem. (I did once see ~~200 MS DNS updates at once, but that geek musta been promoted {or left} because it never happened again.)
My off-the-record advice to senders was "skip MS-Mail, use Gmail." Not that Gmail is fault-free but they do think about things like DNS and IPs. MS may have lost many email customers in that period.