When you first spin up a Microsoft 365 tenant, you get a free onmicrosoft.com domain. Itโs quick, convenient, and great for testing.
But hereโs the catch:
๐ Many organizations continue using it as their primary email domain.
๐ Spammers have been exploiting these shared domains.
Result? Damaged reputation and poor deliverability for everyone. Microsoft has now announced a throttling policy to curb this.
“๐ถ๐๐๐๐๐๐๐ ๐๐๐๐๐๐ ๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐๐.๐๐๐ (๐ด๐ถ๐ฌ๐น๐จ) ๐ ๐๐๐๐๐๐ ๐๐๐๐ ๐๐ ๐๐๐๐๐๐๐ ๐๐ 100 ๐๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐๐ ๐๐๐๐๐๐, ๐๐๐ ๐ ๐๐. ๐ฐ๐๐๐๐๐๐ ๐๐๐๐? ๐ต๐๐ ๐๐๐๐๐๐๐๐ .”
๐ ย ๐๐๐๐๐ ๐๐ก๐ซ๐จ๐ญ๐ญ๐ฅ๐ข๐ง๐ ๐๐จ๐ฅ๐ฅ๐จ๐ฎ๐ญ ๐๐ข๐ฆ๐๐ฅ๐ข๐ง๐:
Oct 15, 2025 โ Trial tenants
Dec 1, 2025 โ < 3 seats
Jan 7, 2026 โ 3 โ 10 seats
Feb 2, 2026 โ 11 โ 50 seats
Mar 2, 2026 โ 51 โ 200 seats
Apr 1, 2026 โ 201 โ 2,000 seats
May 4, 2026 โ 2,001 โ 10,000 seats
Jun 1, 2026 โ 10,001+ seats
If your users are still sending from @tenant.onmicrosoft.com, email deliverability will take a hit. Bookings, notifications, or hybrid routing tied to MOERA domains may break if not updated.
– Purchase and configure a custom domain (yourcompany.com).
– Update all mailboxes to use the new domain as their primary SMTP.
– Re-check integrations (Bookings, notifications, hybrid, SRS).
– Start monitoring MOERA traffic via Message Trace in Exchange Admin Center.
This move is about enforcing best practices and protecting the Microsoft 365 ecosystem. If you havenโt yet migrated off onmicrosoft.com – nowโs the time.
Your email is your brand. Donโt let onmicrosoft.com limit your deliverability, trust, or growth.