Ask HN: Best way to archive 25 years of emails

I have emails from 1997-98 onwards all in one massive inbox, currently on gmail with emclient on Mac as the mail client (there have been probably a dozen services starting from self-hosted in the beginning). I would like to archive the historic mails for the first 25 years, but in a way that's actually searchable and usable in the future (and potentially importable to a new mail client/service) and not in any particular mailbox format that may go obsolete. There is no good reason to hoard them, other than "I feel like doing so". What are the best options, and tools?