Imminent Exchange 2013 Hybrid Mail Flow Interruption


Do you keep your Exchange 2013 Hybrid server on the latest CU? If you don’t; read this article. If you do; read it anyway because you may still be affected! Microsoft recommend that you keep up to date with Exchange CUs if you are running in a Hybrid Office 365 environment, and this is a classic example of why that is the case.

On April 15th 2016, Microsoft will be replacing the Office 365 TLS certificate and the new certificate with have a different Issuer and Subject. This means that if the following scenarios are true, you may face partial loss of mail flow on April 15th if you don’t take remedial action:

  • Your on-premises Exchange servers are running Exchange 2013 Cumulative Update 8 (CU8) or lower.
  • You’ve upgraded the Exchange 2013 servers that handle hybrid mailflow to Exchange 2013 CU9 or higher. However, since upgrading to CU9, you HAVE NOT re-run the Hybrid Configuration wizard (either from the Exchange Admin Center or via the direct download link).

The remedial action is as follows:

  1. If the Exchange 2013 servers handling hybrid mailflow are running Exchange 2013 CU8 or lower, follow the instructions in Updates for Exchange 2013 to install the latest cumulative update on at least one server.
  2. After you install the latest cumulative update, download the new HCW application and run the wizard following the instructions here .

There is also a manual update option for those who do not want to run the HCW again (maybe due to extensive customisation).

More details can be found here:

Thanks god that the 5 Exchange Hybrid servers I just built are running CU11!


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