Exchange Online will Throttle and Block Email from Persistently Vulnerable Exchange Servers

Thursday, March 23, 2023

Microsoft announced that they will begin Throttling and Blocking Email from Persistently Vulnerable Exchange Servers to Exchange Online.

They will begin slowly by blocking OnPremises (hybrid) connections from Exchange 2007 servers to Exchange Online, but plan to include all persistently vulnerable servers soon. A “persistently vulnerable server” is any Exchange server that has reached end of life (e.g., Exchange 2007, Exchange 2010, and very soon, Exchange 2013), or remains unpatched for known vulnerabilities.

If you have any Exchange 2007, 2010, or 2013 servers in your organization that are used for hybrid or SMTP relay, you must make plans to replace or remove them ASAP. You must also keep any Exchange 2016 and 2019 servers up to date with the latest Cumulative and Security Updates, as they are released.

I support this initiative. Organizations using Exchange Servers with known and unpatched vulnerabilities put themselves and their partners at risk. I look forward to seeing it include additional unsupported Exchange Server versions, and I understand their approach of rolling this out slowly and carefully at first.

There are millions of mailboxes in Exchange Online and they have a duty to protect those mailboxes. They know there are 16-year old Exchange 2007 servers currently connecting to their service that haven’t been patched in years and have dozens of known vulnerabilities. 

Microsoft is not forcing anyone to move to Exchange Online. They’re just not going to allow Exchange servers with known vulnerabilities to send hybrid (trusted) emails into their service.

It’s only 2007 for now, but eventually it will be any Exchange Server that is not running the latest or second to latest updates. It’s too risky for everyone.

The table below details the stages of progressive enforcement over time of a persistently vulnerable server:

thumbnail image 2 of blog post titled 
							Throttling and Blocking Email from Persistently Vulnerable Exchange Servers to Exchange Online

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