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Teams Restricts External Collaboration for Tenants That Use MOERA Domains
Imposing restrictions on Microsoft 365 tenants that use a MOERA domain instead of a vanity domain is not unusual. A MOERA (Microsoft Online Exchange Routing Address) is the default onmicrosoft.com domain created when Microsoft provisions a tenant.
A year ago, the Exchange Online team announced that tenants using MOERA email addresses would be limited to sending messages to 100 external recipients per 24-hour period. The logic is familiar. Microsoft believes that tenants using MOERA domains are at higher risk for abuse because the domains are easy to acquire and do not establish an independent reputation in the same way as a vanity domain (like office365itpros.com).
The change will roll out without administrator intervention from mid-September 2026 and should be deployed worldwide by the end of September 2026.
MOERA Tenants Are For Testing
Microsoft’s intent is clear. MOERA domains are for testing. MOERA means Microsoft Online Exchange Routing Address. It exists as a convenience to get a tenant up and running. Organizations should use a vanity domain for production workloads. The restriction on external recipients is now imposed, much to the chagrin of spammers, who commonly used MOERA domains to send unsolicited commercial email in the past. For this reason, many tenants deploy mail flow rules to dump any email received from MOERA domains into quarantine or just drop them altogether with no notification back to the sender.
Roll on to message centre notification MC1463510 (28 August 2026) and we find that Teams intends to follow the same path to impose controls for federated chats with MOERA domains. Microsoft hasn’t published the same kind of precise thresholds as apply in Exchange Online, only saying that “Outbound Teams messages sent to external users will be subject to messaging limits.”
When Teams detects a problem, users will be “temporarily unable to send messages to external users” in federated chats. This indicates that some background function, possibly in the Teams messaging aggregator, will monitor external chats for signs of abusive or high-volume activity and step in to restrict messaging when internal thresholds are exceeded. When federated chat activity drops, Teams will ease the restrictions. Internal chats within the tenant are unaffected.
There’s some value in not documenting the exact point at which Teams will impose restrictions. It keeps spammers guessing and means that Teams can adjust settings if they prove to be too restrictive in production. Teams federated chats rarely generate the same communication volumes as email, so relying on multiple signals instead of a fixed published threshold seems reasonable.
A Step Along a Path to Restrict Unwanted External Collaboration
This development is a continuum of steps that started in 2024 when Teams blocked trial tenants for federated communications. Once again, the idea was to stop spammers who spun up trial tenants before reaching out to other Microsoft 365 tenants via federated chat in social engineering attempts to compromise users. The original block didn’t work as expected because it was easily worked around by purchasing a single license like Teams Rooms Basic. In any case, it was a start.
Since then, Microsoft has provided more sophisticated methods to control federated chat. Trust indicators arrived in October 2025 to highlight potentially problematic external collaborators. The Teams admin center allows tenants to choose from different modes for external collaboration, and new controls were added for the tenant federation configuration introduced in July 2026.
Clear Path Forward
Given that two major Microsoft 365 workloads say that MOERA tenants are not for production use, any tenant that doesn’t use a vanity domain today needs to get with the program and sign up for a domain that they can add as an accepted domain for the tenant in the Microsoft 365 admin center (Figure 1).
Persisting with a MOERA-only tenant doesn’t make sense. It’s a path to greater restriction because the only thing that will happen in the future is for Microsoft to introduce blocks and thresholds like those in Exchange Online and Teams to confound spammers. Why anyone would want to risk hitting those blocks when a vanity domain costs so little and avoids the problem completely is something that confounds me.
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