Re: I felt your pain
My email is a veritable treasure trove of solutions, software licenses, downloads, URLs, contracts, documents, evidence, links, history, etc.
There's a reason I keep it, and it's not that there are millions of messages in there. It's that I can find THAT ONE RIGHT NOW without having to worry about how to do that.
Sure, I rarely refer to my 1997 Hotmail imports, but the point is that when I need to, it's right there. Everything from old school friends to orders to documents I wrote which are still relevant to catching people out when they say "That's not what we said". Personal, work, my old businesses I used to run, everything.
And it's a great source of spam vs real email tagged properly, for classification purposes for training spam filters.
Literally haven't deleted an email in 20 years. And literally use - and keep - Opera just for its insta-search across those 20 years of IMAP, POP, etc. accounts.