Please note, Migration Monster remembers what items have been migrated to the destination. If you delete items on the destination and then run the project again it will not attempt to re-migrate them unless you delete the mailbox within the Migration Monster project, delete entire project or select the mailbox and run the Clean Migration option against it. The Clean Migration option allows our system to copy all items again. In this situation, we would also recommend you delete and re-create the destination mailbox to prevent duplicates at the destination.


On the mailbox page the "Source Estimate" column is a best endeavour attempt to calculate the number of item that are available to migrate . Many of our competitors do not attempt a source count and instead report the number of items migrated off the source. We feel this hides the true migration picture. We provide this field as it provides a good means of highlighting where potential issues could be as you can then see source and destination counts side by side.  If there is a mismatch please also consider the following:-



If Migration Monster is showing a difference between the source and destination, please consider the following:-




  • First of all, make sure the migration completed fully and check the error logs for an explanation of any failed items. For example, It may be that an item was too large to migrate or corrupted.

  • Check to see if the shortfall can be explained by adding the number of non-transferable items (displayed in the non-transferable item column) to the number of items transferred to the destination. 

  • If there are errors in the error log try running the "retry errors" function or run the entire project again (running the project again will deduct a project pass from the 10 you receive as standard). From the projects (Home) page view all errors (both system and mailbox) are shown and from the mailbox view , just the errors that relate to specific mailboxes ( no system wide errors are displayed).

  • Check to make sure that source mailbox items (or folders containing items)  were not deleted during the migration.

  • Check to see if the source mailbox has any limiting permissions set against the folders.

  • Check to see if additional items were received by the source during the migration.


If a difference can be seen within the actual mailboxes themselves, please consider the following in addition to the above:-


  • Check to make sure that the items have not been manually moved or deleted by someone logging into the destination mailbox

  • Check to make sure that items have not been automatically archived on the destination mailbox.

  • Check to make sure that items have not been filtered by any mailbox filtering/rules.

  • Check to make sure  that items have not been filtered by a mailbox connector

  • Check to make sure that items have not been moved to the Junk folder

  • Check to make sure that items have not been moved to another folder



Please also have a read of this article:-


https://migrationmonster.freshdesk.com/solution/articles/25000020038-ms-outlook-how-to-show-a-count-of-all-items-within-each-folder-rather-than-the-default-unread-


If all the above has been considered and you still have a unexplained mismatch,  please raise a ticket for further assistance.