Certainly. It is not an issue caused by VM, as far as we can tell. The most likely cause is a badly configured email client (in this case Outlook) using IMAP as the mail protocol for receipt of mail; which is set to purge automatically or a manual instruction has been issued by the user to purge mail for the specific period, often accidentally. If it were VM's issue we would see this issue repeated on a scale that would be hard to dismiss. And we do not see it on that scale. Most of the time when we see this the email client responsible is on an Apple device, but not exclusively so. Apple devices when IOS is upgraded do strange things.
The mails are lost forever. VM do not archive them once the delete/purge command is issued by the email client. The issue with IMAP is that the mail is not downloaded to the email client (as it is with POP). IMAP just gives the email client a view onto web mail. The mail is stored there. That is how the IMAP protocol works to ensure that what is done in one place is reflected across all the devices that are used to view email provided the folders on the client and web mail are properly mapped to one another.
It is always the responsibility of the user to back up mail. Relying on the servers used by any ISP is always risky. They might have had a catastrophic failure for other reasons. VM's haven't (as far as we know, and we would know if that was the case).
@Ryan_N
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