Don't you have shadow copy?

Unfortunately no, I backup database but never thought about backing up emails. Sounds very stupid now.

Deleted items?

That account was a catch-all and used to get spam mail as well - around 20-30 daily. I would typically select all spam mail and delete. Since I never opened the spam mail, it would show up as Unread email in Deleted folder, so I would go in Deleted folder and Delete All. Been doing that for several years, but someone screwed up this time and I guess Deleted All in Inbox.

For recovery, should I be looking for deleted .grp files and would just copying them back in Inbox restore those emails?

Mike, unfortunately if you don't have a backup system which is backing up the user's GRP files they will likely no longer be present on the server. Do you have an older account backup you can restore from? Ultimately though you're looking for GRP files which will contain a day's worth of email. If you need help getting them restored please don't hesitate to submit a ticket with us.