Microsoft Limits Free “onmicrosoft” Email Domains to Stop Spam
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When you set up Microsoft 365, you automatically get a free email domain that looks like yourcompany.onmicrosoft.com. It’s the easiest and quickest way to start testing emails and accounts. However, here’s the catch: many businesses never move away from this “starter” domain.
That has caused problems. Because thousands of companies share the “onmicrosoft” name, spammers often abuse it to send junk mail. Not to mention, this even caused genuine emails to get blocked or flagged.
To fix this issue, Microsoft is putting strict limits in place. Starting October 15, 2025, organizations that still use onmicrosoft.com as their main domain will only be able to send 100 external emails per day. Anything above that gets blocked with an error message. Emails sent inside the same company will still work as normal.
The rollout will happen in stages, depending on company size. For example, trial accounts get hit first, while the biggest organizations won’t see limits until June 2026. Microsoft says these free “onmicrosoft” domains should only be used for testing, not for regular email. Therefore, your business should:
- Buy their own custom domain (like yourcompany.com).
- Add that domain to Microsoft 365.
- Switch user email addresses to the new domain.
- Update login details and apps that use the old addresses.
In short, Microsoft wants companies to look professional, protect their brand, and keep email delivery reliable. Using a custom domain not only avoids these new limits but also ensures your messages don’t get lost in spam filters.
The company has further noted, “Announcements for each stage of the rollout will be made one month before via Message Center to all customers meeting the seat count criteria. All customers who are using their MOERA domains are encouraged to start planning and migrating today.“
