Postmortem10 min read
How Microsoft 365 decides which tenant email belongs to
A new mail-flow rollout made Microsoft 365 attribute every customer's mail to our tenant. The undocumented rule behind it, and the fix.
Mailprotector·Engineering Team
$ ls archive/2026/06/
June 2026
2 posts this month.
- SMTP3 min read
HELO, world!
Why an email security company is starting an engineering blog, and what we plan to put here.
Ben Hathaway·Chief Technology Officer
