EOL - Troubleshooting Exchange Online Mailbox Migration Speeds

Working for a client we run into numerous issues where we were seeing sluggish performance when migrating mailboxes to Exchange Online, here are a few of the troubleshooting steps we went through. (The actual was being caused by some barracuda load balancer devices which we had to remove out of the migration path.) 


  • Ensure the Exchange servers are patched with the latest CU
  • Ensure all flood mitigation, SSL offload, traffic inspection and any IP connection limits are removed from the firewall connections to mail.domain.com (including TMG)
  • Review Migration endpoint and ensure that MaxConcurrentMigrations are set to a reasonable number for your infrastructure, currently using 35 and 25 MaxConcurrentIncrementalSyncs (use Get-MigrationEndpoint | fl to check.)
  • #Export all MoveRequest Stats to CSV and review for errors and information alerts or TransientException errors. - Get-MoveRequest | Get-MoveRequestStatistics  | Export-CSV Get-MoveRequestStatistics.cs
  • Test Removing any load balancer devices from the migration path so that only a single CAS server is used.
  • Check Firewall and CAS server timeouts - https://blogs.technet.microsoft.com/exchangechallengeaccepted/2017/04/15/what-is-keepalivetime-used-for-in-regards-to-exchange/
  • If you are seeing TransientException or '‘Informational: The request has been paused temporarily because the mailbox is locked. The Microsoft Exchange Mailbox Replication service will attempt to continue processing the request after xx/xx/xxxx’ errors try modifying the MRS timeout values on the Exchange servers. The below config file value should be modified. 
    (Make a copy of the config file (Take a backup) before modifying the files.)
      Find the MRS config file under (Default location) : C:\Program Files\Microsoft\Exchange Server\V15\Bin\MSExchangeMailboxReplication.exe.config
        Find the below section in the config file (MrsProxyClientHttpsBinding) and modify the receiveTimeout to 5 minutes from 50 seconds.
          Before modification
                   <binding name="MrsProxyClientHttpsBinding" 
                              receiveTimeout="00:00:50" 
                                sendTimeout="00:00:50">
                           <reliableSession ordered="true" />
                             <textMessageEncoding>
                                <readerQuotas maxArrayLength="1048576" 
                                                maxStringContentLength="1048576" />
                                   </textMessageEncoding>
                                     <httpsTransport authenticationScheme="Negotiate" 
                                                      maxReceivedMessageSize="1048576" 
                                                        allowCookies="true" />
                                         </binding>
                                         </customBinding>
                                      After modification
                                               <binding name="MrsProxyClientHttpsBinding" 
                                                          receiveTimeout="00:05:00" 
                                                            sendTimeout="00:00:50">
                                                       <reliableSession ordered="true" />
                                                         <textMessageEncoding>
                                                            <readerQuotas maxArrayLength="1048576" 
                                                                            maxStringContentLength="1048576" />
                                                               </textMessageEncoding>
                                                                 <httpsTransport authenticationScheme="Negotiate" 
                                                                                  maxReceivedMessageSize="1048576" 
                                                                                    allowCookies="true" />
                                                                     </binding>
                                                                     </customBinding>
                                                                  Make the change on all the Exchange servers and restart Microsoft Exchange Mailbox Replication Service.

                                                                  • Review MRS Throttling - https://docs.microsoft.com/en-us/previous-versions/office/exchange-server-2010/ff963524(v=exchg.141)
                                                                  • Create a new Mailbox DB and perform internal moves of troublesome mailboxes



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