2 Mailboxes are consistently failing to backup with the error Failed to process mailbox. Error message [The server cannot service this request right now. Try again later.]]

Hi @Oriium 

Hope you’re well.

Any idea how big these particular mailboxes are? 

The error generally means throttling is occuring: https://docs.microsoft.com/en-us/exchange/client-developer/exchange-web-services/ews-throttling-in-exchange

A way we can usually work around this is to create additional service accounts / azure apps as per: https://documentation.commvault.com/commvault/v11/article?p=125313.htm 

If you need assistance with this, I’d suggest raising a support incident and we can review it further / provide remote guidance.

Thanks,

Chris