I'm synchronizing Office 365 mail folders via the Office 365 REST API by doing a GET on me/MailFolders/{folder_id}/messages. For two different accounts, I've recently been getting 500 responses to these GETs with the error code ErrorMessagePerFolderCountReceiveQuotaExceeded and error message "The number of received messages has exeeded the quota for the folder." (Typo theirs, not mine.)
I can't find any documentation on this error. What does it mean? What should I do to fix this situation?
When you do a sync to an Exchange folder via the Outlook REST API, you pass it a sync token. In response, the API returns a new sync token and a set of changes. And the client is expected to send the new token back with their next sync request.
With most systems that support sync, using a stale sync token (i.e. one that has been sent to the server once) in a subsequent request will generally just succeed with no problems. And Exchange appears to work like that... for the first 999,999 times you do it. On the 1,000,000th time (and each time thereafter), you get ErrorMessagePerFolderCountReceiveQuotaExceeded. This is (I think) because Exchange keeps track of each token that it's given out and updates the token in its store each time it's used for sync. If a client uses a stale token, Exchange views it as a new client and adds that stale token as a new entry in its list of active tokens. That active token list can have at most 1,000,000 entries. ErrorMessagePerFolderCountReceiveQuotaExceeded is the cryptic error indicating that Exchange's active token list has overflowed.