As per here - Managing Log Files - Veeam Backup for Microsoft 365 Guide

You can check the logs in - %ProgramData%\Veeam\Backup365\Logs\<organization_name> folder

This is when data is retrieved and should show the accounts being used.  There are other logs for when the backups happen which should also show the accounts being used as well.

Thank you for the quick reply…

So, I did open the Veeam.Archiver.Proxy log while the job is running and I see multiple Warnings and Web errors as listed below. When looking at the individual items in the Veeam Backup GUI, I do see that items are being backed up successfully. I did look at previous logs before adding the additional Backup Accounts, and it also shows the same Warnings and Web errors.

Are the Warnings and Web errors listed indicative of an issue with the accounts themselves?

5/25/2022 9:41:30 AM  102 (1504) Throttling count for VeeamO365Backup01@rdvcorp.com: 7
5/25/2022 9:41:30 AM  102 (1504) Warning: The remote server returned an error: (429).
5/25/2022 9:41:30 AM  102 (1504) Warning: Web request failed
5/25/2022 9:41:30 AM  102 (1504) Warning: Unable to process request. Server cannot service the request
5/25/2022 9:41:30 AM  102 (1504)  Waiting before next processing attempt: 00:05:02...
5/25/2022 9:41:31 AM   72 (1076) Web error occurred: 429 TOO MANY REQUESTS (status: ProtocolError)
5/25/2022 9:41:31 AM   72 (1076) Throttling count for VeeamO365Backup01@rdvcorp.com: 8
5/25/2022 9:41:31 AM   72 (1076) Warning: The remote server returned an error: (429).
5/25/2022 9:41:31 AM   72 (1076) Warning: Web request failed
5/25/2022 9:41:31 AM   72 (1076) Warning: Unable to process request. Server cannot service the request
5/25/2022 9:41:31 AM   72 (1076)  Waiting before next processing attempt: 00:05:13...
5/25/2022 9:41:51 AM    5 (4136)  Trying to resume...
5/25/2022 9:41:51 AM    5 (4136)  Web error occurred: 429 TOO MANY REQUESTS (status: ProtocolError)
5/25/2022 9:41:51 AM    5 (4136)  Throttling count for VeeamO365Backup02@rdvcorp.com: 28
5/25/2022 9:41:51 AM    5 (4136) Warning: The remote server returned an error: (429).
5/25/2022 9:41:51 AM    5 (4136) ClientRequest: Microsoft.SharePoint.Client.ClientRequestWrapper
5/25/2022 9:41:51 AM    5 (4136) Warning: Web request failed
5/25/2022 9:41:51 AM    5 (4136) Warning: Unable to process request. Server cannot service the request
5/25/2022 9:41:51 AM    5 (4136)   Waiting before next processing attempt: 00:00:34...
5/25/2022 9:41:54 AM  111 (2216)  Trying to resume...
5/25/2022 9:41:54 AM  111 (2216) Synchronizing web changes...
5/25/2022 9:41:54 AM  111 (2216) Web error occurred: 429 TOO MANY REQUESTS (status: ProtocolError)
5/25/2022 9:41:54 AM  111 (2216) Throttling count for VeeamO365Backup03@rdvcorp.com: 15
5/25/2022 9:41:54 AM  111 (2216) Warning: The remote server returned an error: (429).
5/25/2022 9:41:54 AM  111 (2216) ClientRequest: Microsoft.SharePoint.Client.ClientRequestWrapper
5/25/2022 9:41:54 AM  111 (2216) Warning: Web request failed
5/25/2022 9:41:54 AM  111 (2216) Warning: Unable to process request. Server cannot service the request
5/25/2022 9:41:54 AM  111 (2216)  Waiting before next processing attempt: 00:00:35...
5/25/2022 9:41:56 AM   54 (5236)  Trying to resume...

Not with the accounts themselves no as I read this as MS seeing too many connections and then throttling the accounts as per the lines -

5/25/2022 9:41:54 AM  111 (2216) Web error occurred: 429 TOO MANY REQUESTS (status: ProtocolError)
5/25/2022 9:41:54 AM  111 (2216) Throttling count for VeeamO365Backup03@rdvcorp.com: 15

To achieve automatic user adding to Veeam 365 backup, I suggest to read this interesting article:

https://www.veeam.com/blog/automate-auxiliary-accounts-backup-office.html

Thank you all for the swift attention to this question. The article on “Auxiliary Accounts” looks very interesting. I am currently backing up only 1 organization with an average total of 1250 objects so we are quite small currently. I just created the additional backup accounts because i noticed a significant delay (from normal 3 hours to 12 hours) in backing up a user’s OneDrive that jumped to a couple hundred GBs. I will monitor the backup performance with these added manual backup accounts.

Glad our information was useful to you and we are always here to help.