Invitations for our tenant are blocked due to suspicious activity

The block on sending B2B guest invitations due to “suspicious activity” and the 403/Forbidden errors cannot be removed through configuration in the tenant. This type of restriction must be handled directly by Microsoft support.

Required actions:

1. Open a support ticket with Microsoft
   • Sign in to the Microsoft 365 or Azure portal with a Global Administrator or other support-eligible admin account.
   • Create a new support request describing:
     • The exact error messages:
       • “Invitations are blocked for this directory due to suspicious activity. Please contact Microsoft support for help. Error: 403 Forbidden ErrorCode: Forbidden”
       • “Insufficient privileges to complete the operation” when sending invitations.
     • The approximate number of invitations sent and that the tenant is now blocked from sending B2B invitations.
   • Ask specifically for the block on B2B guest invitations to be investigated and removed.
2. Be prepared for identity and security verification
   • Support may route the case to internal security/data protection teams to verify tenant ownership and confirm that the activity was legitimate before removing the block.
   • Provide any requested business documentation and context about the bulk invitations.
3. After Microsoft removes the block
   • Test by inviting a single guest user via the Microsoft Entra admin center (Entra ID → External Identities → All users → New guest user).
   • If invitations still fail, have an admin verify:
     • External collaboration settings and collaboration restrictions (allow/block lists) under External Identities → External collaboration settings.
     • Cross-tenant access settings if inviting users from specific organizations.

Because this is a service-side protection mechanism triggered by suspicious activity, only Microsoft support can clear the block and restore normal B2B invitation capability.

References:

• Troubleshoot common issues with Microsoft Entra B2B collaboration
• What is Microsoft Entra B2B collaboration?
• Allow or block B2B collaboration with organizations
• Design Tenant Configuration
• Discover the current state of external collaboration in your organization