Microsoft 365 Objects Fail to Be Backed Up Referencing Error 429 (4373844)

Microsoft 365 Objects Fail to Be Backed Up Referencing Error 429

Microsoft 365 backup jobs complete with warning because, one or more items (sites, account, e-mails, etc.) fail to be backed up. When reviewing the job binary log, entries reference error 429:

Exception occurred - Reason: The remote server returned an error: (429)

Similarly, on the trace logs, error 429 will be listed as the reason for exceptions:
 

Level	Module	Thread	Id	Error	Time	Message
2	OFFICEUT	13576	415	0	72327784692	Error reading data
4	OFFICEUT	13576	4	0	72327784692	Error from in library - [backup time] [object]: Exception occurred - Reason: The remote server returned an error: (429).
5	LOGGING	13576	9	0	72327784692	Found context object!

 

Error 429 is issued by Microsoft Graph API:

Throttling limits the number of concurrent calls to a service to prevent overuse of resources. Microsoft Graph is designed to handle a high volume of requests. If an overwhelming number of requests occurs, throttling helps maintain optimal performance and reliability of the Microsoft Graph service.

Reducing the concurrent number of requests made by backup jobs using the NetVault Plugin for Microsoft 365 should alleviate the problem; however, there are conditions that cannot be controlled by the backup software. For instance, there could be requests performed by users accessing Microsoft resources. Consequently, the backup of some objects could still fail; however, the possibility that the same objects won't be backed up the next time the job runs is unlikely, but still plausible. Reduce the number of concurrent request by making the following changes:

• If multi-stream is enabled, reduce the number of streams or disable it.
• Schedule Microsoft 365 backup jobs to run at different times.