To avoid accidentally deleting useful emails while “Ctrl-A-ing”, could they have run a search by sender or some other criteria first? Then only delete the search results.
In the email client? Probably yes, if they know how. This was a very long time ago, early 2000s, and the email client was the dreaded Lotus Notes software.
I had to use that client recently. I can't believe it doesn't even have a proper email search function. Best you can get is ctrl-f on the open page or sorting all your email alphabetically.
