tinyapps.org / blog
TL;DR: Since at least February 2020, Microsoft's Autodiscover service has incorrectly routed the IANA-reserved example.com to Sumitomo Electric Industries' mail servers at sei.co.jp, potentially sending test credentials there.
Problem
While setting up [email protected] as a dummy account in Outlook (on both Windows and macOS), Outlook consistently auto-configured it to use imapgms.jnet.sei.co.jp (IMAP) and smtpgms.jnet.sei.co.jp (SMTP) despite example.com being an IANA-reserved domain that should not resolve to real services.
The same behavior appeared on different machines, profiles, networks, and DNS resolvers, including a newly provisioned Windows 365 Cloud PC:
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Confirmation
DNS verification
Confirm that example.com has no DNS records pointing to sei.co.jp :
% dig MX example.com +short 0 . % dig CNAME autodiscover.example.com +short (no response) % dig SRV _autodiscover._tcp.example.com +short (no response)
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