Exchange CAS autodiscovery failed - trying to backup guest accounts

[sbk]

Problem started after updating to Veeam version 5.
Currently on Veeam version 5.0.0.1070

I've got a job that backs up our instance of Exchange Online - the job has failures because for some reason its attempting to backup guest accounts. When it hits the guest account in the discovery process the job gives the error: "<date & time> :: Processing mailbox <guest account that is not in our domain> failed with error: Exchange CAS autodisovery failed: InternalServerError". Prior to updating to version 5, this error did not happen and no guest accounts were ever attempted to be backed up.

The guest accounts that are being referred too in the error are valid, in the sense that they are in our Azure Active Directory as a guest account from being added to externally accessible SharePoint online sites (they are our clients). They are not valid in the sense that they do not have mailboxes and have nothing to do with Exchange Online.

The job is setup as follows:
Name: Exchange Backup > Backup the following objects: [our organization] > Process [Mail/Archive]

I've now had a ticket open for a couple of weeks and support still seems to be confused on the problem and hasn't been able to offer much in terms of a resolution. We have many guest accounts that are added all the time - so having to exclude them manually after seeing the error each day would be incredibly time consuming and would quickly result in a very large exclusion list that I wouldn't know how to maintain over time.

Any suggestions are appreciated - not sure if anyone else is having this same issue after the update.

Ticket number: 04537583

[Polina]

Hi Shawn,

Thanks for reporting on this issue. Can't promise a quick hotfix yet, but I'll ask to escalate your case to RnD.

[sbk]

Just wanted to provide an update on this issue. The problem was resolved after I was provided a hotfix - all is working as expected again.

[dirtydave]

How do I get this hotfix? I am having the same problem. I told the job to exclude the group the guest users belong to but that didn't exclude the users because the job still generates errors trying to backup their non-existent mailboxs.

[sbk]

I would reach out to support and reference this post. I do still have the hotfix that they gave me I'm just not sure if it would be ok for you to install it without knowing if its compatible with your environment, etc.