CloudAlly Microsoft 365 backup warning: Mailboxes of some accounts are unavailable

CloudAlly Microsoft 365 backup warning: Mailboxes of some accounts are unavailable

Machine-distilled from a resolved support ticket on 2026-09-28. Source ref: 9c8599dce65a. Verify before relying on it.

Applies to: CloudAlly SaaS backup of Microsoft 365 Exchange mailboxes. Not version specific.

Symptom: Microsoft 365 Exchange backup tasks on the CloudAlly platform complete with the warning or error 'Mailboxes of some accounts are unavailable'.

Cause: The backup task still includes one or more accounts whose mailboxes no longer exist or are no longer available in Microsoft 365 (for example the user was removed, the mailbox was deleted, or the licence was taken away). The backup cannot reach those mailboxes, so the task reports them as unavailable.

Resolution: 1. Open the backup task report and note which accounts are listed as unavailable.

2. In Microsoft 365, check whether each mailbox still exists and is licensed.

3. In the CloudAlly backup task, for each affected account:

a. Pause the account if the mailbox may be restored or reactivated later and you want to keep the existing backup data.

b. Delete the account from the backup task if the mailbox has been permanently removed and no longer needs to be backed up.

4. Wait for the next scheduled backup run and confirm it completes without the warning.