In case your mailbox export request should stall or restart indefinitely often it is caused by Exchange detecting your disk as too slow. The default values are defined as 10 and 20 ms for a healthy disk situation. You can change these values if needed:
Go and edit C:\Program Files\Microsoft\Exchange\v15\bin\MsExchangeMailboxReplication.exe.config with elevated privileges.
At the bottom you find the keys for:
MdbFairUnhealthyLatencyThreshold
MdbHealthyFairLatencyThreshold
I changed them to 100 and 200 ms due to an iSCSI disk having peaks of almost 200 ms when exporting a mailbox.
<appSettings>
<!-- Mdb latency health threshold values in msec. Valid range is from 0-1000. -->
<add key="MdbFairUnhealthyLatencyThreshold" value="200"/>
<add key="MdbHealthyFairLatencyThreshold" value="100"/>
<!-- Maximum delay that WLM returns under "Fair" database resource health in msec. Valid range is from 0-60000 -->
<add key="MdbLatencyMaxDelay" value="60000"/>
<add key="LogEnabled" value="true" />
<add key="LogDirectoryPath" value="%ExchangeInstallDir%Logging\MailboxReplicationService\" />
<add key="LogFileAgeInDays" value="30" />
<add key="LogDirectorySizeLimit" value="100MB" />
<add key="LogFileSizeLimit" value="10MB" />
<add key="LogCacheSizeLimit" value="2MB" />
<add key="LogFlushIntervalInSeconds" value="60" />
</appSettings>After the change do not forget to restart MSExchangeReplication service.