When moving a SmarterMail installation from one server to another it is best to minimize the downtime. When a SmarterMail install has many GigaBytes or more of data this can take a long time to copy from one server to another and cause a long downtime.
To help minimize the downtime and speed up the migration process, it's a good idea to use Robocopy to copy the data over a few days before the move and then use it again to ONLY copy the changed data. Doing the bulk of the migration ahead of time, then simply copying over just the changed data means that final step in the migration process is much smaller and will minimize the downtime.
To do this follow the command below.
C:\>Robocopy [source] [destination] /MIR /ZB /R:1 /W:3
This will mirror the data and then will retry once and wait 3 second before attempting a retry if there are any connection issue.
Here's an example:
C:\>Robocopy C:\SmarterMail\Domains \\SmarterMail_New\SmarterMail\Domains /MIR /ZB /R:1 /W:3
NOTE: When using the /MIR command this will overwrite any data in the destination folder that does not match the source folder.
For more commands on Robocopy please see Microsoft documentation