Important news for organizations still using only the default onmicrosoft.com domains.
From mid-September 2026, Teams will introduce outbound external messaging limits for organizations that haven’t configured a custom domain.
In practical terms, affected organizations may face limits on the number of messages they can send to external users in Teams.
About the Teams External Messaging Limits News
The change is designed to reduce spam, phishing, and other abusive activity associated with default onmicrosoft.com tenants. The protection will be enabled by default.
- External Teams messaging may be temporarily restricted when the applicable limit is reached.
- External messaging will automatically resume once activity falls below the applicable threshold.
- Microsoft has not publicly specified the exact messaging threshold for this Teams protection.
- ☑️Internal Teams messaging and collaboration will continue to work normally.
- ☑️This specific change does not target organizations with a custom domain configured.
If you’re still using the default domain for production, now is a good time to prepare:
→ Check whether onmicrosoft.com is your organization’s only domain
→ Add and verify a custom domain if needed