Strange Migration Batch Error

During a recent remote migration batch from on-premises to Exchange Online, I noticed a high number of failures that I couldn’t explain. This prompted me to investigate the single Exchange 2019 server that was set up as a hybrid server between the Exchange 2013 environment and Exchange Online. Let’s take a dive into this strange migration batch error.

Upon logging in, I discovered that all Microsoft Exchange services were stopped. This was a major issue, as it meant that there was no mailflow between the Exchange on-premises environment and Exchange Online.

I attempted to start the Microsoft Exchange Active Directory service, but it immediately stopped. This was unusual, and I discovered an event 1092, MSExchangeADTopology, in the event viewer.

I wondered how this was possible, as the server had been running smoothly for several months. After examining the Active Directory Sites and Services, I noticed that the subnet to which this server belonged was not added as a subnet or assigned to a site.

After a Domain Admin added the subnet and assigned it to the correct site, the Exchange 2019 server began functioning properly once again.

However, we are still unsure why the server was able to run for so long without any issues, or when the subnet was removed from Active Directory Sites and Services. Unfortunately, logging is deleted after 24 hours, which is a valuable lesson for this customer. Therefore, we were unable to determine when this issue first started.

So, there you have it, a strange migration batch error solved. Did you encounter any rare errors during your migration? Let me know in the comments.