Issue

Some times, the performance of EWS backup/restore may run slow.


Summary

To improve slow backup & restore performance of EWS backups sets (mail level backup for large Exchange on-premise), following tweaking parameters can be adjusted:
Three tweaks that might help speeding up the EWS backup sets:
In DS-User > Setup > Configuration > Advanced > Miscellaneous change the values mentioned below as follows:

Office365RequestRetry set it to 3 (this reduced the restore time in one particular scenario from 45 minutes to 60 seconds).

ExchangeOnlineExcludeGroupMailboxes set it to No (this reduced the listing of mailboxes when expanding the virtual share tree from 1 hour to 5 seconds)

ExchangeOnlineFilterListingsBySet set it to Yes (this improved backup speed by 15%).