throttling and blocking of out-of-date on-premises Exchange Servers

Hi All,

Microsoft has published several Blog Articles on the Exchange Team Blog, that they will throttle then block old and unpatched on-premises Exchange Servers.

• Throttling and Blocking Email from Persistently Vulnerable Exchange Servers to Exchange Online
• Update on Transport Enforcement System in Exchange Online
• How to pause throttling and blocking of out-of-date on-premises Exchange Servers

Timeline

They started in Summer 2023 with Exchange 2007. Now in February 2024 they start to block Exchange 2013 - Extended Support ended on 11 April 2023

Throttling and Blocking stages

SMTP Error codes

Microsoft has documented these SMTP Error codes for Throttling and Blocking

Throttling

450 4.7.230 Connecting Exchange server version is out-of-date; connection to Exchange Online throttled for n mins/hr.

Blocking

550 5.7.230 Connecting Exchange server version is out-of-date; connection to Exchange Online blocked for n mins/hr.

Reporting

How do i know that i am affected?

In Exchange Admin Center you can find a Report > Mail flow reports > Out-of-date connecting on-premises Exchange servers

Obviously my OnPrem Exchange Server is fully patched and i have no outdated Exchange Servers running

Here is a Picture from a the Exchange Team Blog how it could look like

You can pause the Enforcements directly here

There are also some new commandlets in ExchangeOnlineManagement PowerShell Module

Show the Report in Powershell

Connect-ExchangeOnline -ShowBanner:$false
Get-OnPremServerReportInfo

Show Enforcement pause

Get-TenantExemptionInfo -BlockingScenario UnpatchedOnPremServer

Add Enforcement Pause

New-TenantExemptionInfo -BlockingScenario UnpatchedOnPremServer -NumberOfDays 90
Get-TenantExemptionInfo -BlockingScenario UnpatchedOnPremServer

Regards
Andres Bohren