I have problems with mailbox move from our hybrid exchange 2010 to EXO. I can see in the moverequeststatistics report this error "Transient error FolderNotmappedTransientException has occurred The system will retry". As I can see in the log the Exchange Mailbox replication service tried continue the move operation a lot of times but no go . Mailbox move was failed. I tried to remove the mailbox move request and recreate it but every time ( run always failed with this error by 87%) failed. Did someone meet same error message?
Finally the mailbox was sucessfully moved to the EXO. The user mailbox exceded its mailbox quota and maybe some items were corrupted. I moved it to another mailbox database which quota size is unlimited. A few days later the mailbox was sucessfully moved into EXO. First just try to increase the mailbox quota if it will not helped move it to another mailbox database.