Excessive traffic and processing of mailbox with many deleted items

[mrowell]

We had a user that a few days ago deleted around 200K emails (20GB) from their Exchange Online account. The initial VBM365 job was processing the mailbox for over 20hrs, downloading at 50Mbps.

Support advised I exclude that mailbox from our primary Mail job and create a new job for just that mailbox to the same backup repository. The initial full back ran with expected traffic for about 3hours, before returning to the 50Mbps traffic again.

The logs looks like it is processing 100 emails every 5mins. This suggest that it will take another 60hrs to complete the job. This seems like an exorbitant amount of time and bandwidth.

A different on-premises MS 365 backup solution we are evaluating processed our entire tenant, including this mailbox, with 200K deletions, in 30mins.

Support said this is expected behaviour when the sync between the VBM365 can be disrupted by such large scale changes in the source mailbox.

I can't understand why this isn't a bug. There is no way that VBM365 should download over 800GB of data to fix a previously 50GB, now 25GB, mailbox. If the sync is broken, just download the entire mailbox again, and sort it out locally.

Case # 05615772

[Mildur]

Hi Marcus

Thanks for the case number.

Support said this is expected behaviour when the sync between the VBM365 can be disrupted by such large scale changes in the source mailbox.
I can't understand why this isn't a bug. There is no way that VBM365 should download over 800GB of data to fix a previously 50GB, now 25GB, mailbox. If the sync is broken, just download the entire mailbox again, and sort it out locally.

That shouldn't happen (download 800GB when you delete 20GB) and looks to me like a bug. In the last comment, your support engineer also have confirmed that it's most likely a bug.
Please keep working with support. If it's a bug, your support engineer will escalate it to R&D to be fixed.
If you are unhappy on how the case goes on, please also use our "Talk to a Manager" form.
https://www.veeam.com/kb2320

Thanks
Fabian

[mrowell]

This issue was resolved with help from Support. With Support's guidence we rebuilt the local persistent cache for the Object Repository and inititiated a full backup. It took over night but the mailbox was eventually backed up and is now without any ongoing issues.