If your organization is currently getting throttled / blocked by Exchange Online, you must update your connecting Exchange Server to at least October 2025 Security Update level (which will stop the t...
Updated Nov 10, 2026
Version 12.0
Blog Post
10 MIN READ
Throttling and Blocking Email from Persistently Vulnerable Exchange Servers to Exchange Online
This is really frustrating when you have situations where companies use On-Prem hosted ERP systems and they have limitations to use SMTP relay puts admin in a
tough situation not been able to help with the essential business requirement like Email Flow. Our on-prem exchange server is 2013 and all our mailboxes are migrated to Office 365 and looking to migrate the Email relay also to office 365 and it has issues which is being looked at to resolve. We have a valid SSL certificate and seeing issue for inbound emails when sent from ERP to inside the organization it fails showing this throttle error. Hope Microsoft can understand this and provide a solution.