Configuring sufficient concurrent MAPI sessions for Folder Sync

Last published : Apr 17, 2026
Folder Sync makes a MAPI connection to the Exchange server to enable it to read the folder structure within each mailbox and the items within each folder. To avoid MAPI errors for the number of concurrent mail threads, you can do one of the following, depending on the version of Exchange Server:
  • Increase the number of allowed MAPI sessions.
  • Remove the MAPI session throttling that the Exchange servers perform for concurrent mail threads.
Follow the procedure that applies for your version of Exchange Server.

Table: Setting the permissions for the Folder Sync service account on the Exchange servers