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Xadean's Empirical Musing > Posts > Fail to Migrate On-Prem Exchange Mailbox to Online
February 10
Fail to Migrate On-Prem Exchange Mailbox to Online


  • Office 365 – Exchange Online (All users' mailboxes homed)
  • On-Prem Exchange with hybrid configuration enabled
  • On-Prem Active Directory (AD)
  • Directory Synchronization (AD Connect)
  • Active Directory Federation Services (AD FS)

Error Encountered

After running the "Migrate to Exchange Online" wizard and selecting all the default actions, encounter the following error after selecting the configured Mailbox Replication Service (MRS) Proxy:


"Error: The connection to the server '' could not be completed".



The only thing that had changed in the environment prior to experiencing this issue was SSL certificates throughout the infrastructure had been changed for on-prem Exchange, ADFS, and MSFT Online Federation. This catalyzing event was the root cause.


Add a new Migration Endpoint and associate an administrator with the appropriate privileges. Note that you will be unable to delete existing migration endpoints that are associated to migration batch jobs that have previously ran. Therefore, you must delete those associated migration batch jobs first in order to remove any existing migration endpoints. Once you have created the new migration endpoint, you will be able to select it in the migration batch task. After doing this, I was able to successful migrate on-prem user mailboxes to online.


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