Error flagged from ODM mail migration :
Cannot migrate the rule 'XYZ': Error resolving folder: The referenced folder does not exist.
ODM is unable to properly resolve on some specified conditions in this affected mail rule 'XYZ' at source.
Please verify on all specified conditions in this affected mail rule 'XYZ' at source, ensuring them to be similarly resolvable at target, because in order for ODM to be able to successfully migrate this mail rule, the mail folder name which is referenced by any specified condition will need to pre-exist at target, else this mail folder will need to get manually created first, before using ODM to migrate this whole mailbox again.