I'm migrating from two very old (the oldest from 2004) Gmail accounts to one iCloud Mail. Unfortunately both accounts have, together, around 30k uncategorised emails in their inbox, from which probably at least 70% could be deleted.
My goal is to have those email accounts completely empty and clean, and check them every once in a while in case something important (old acquaintance, etc.) pops up, or in case I use a service linked to that account (which I would change to my new email).
I gave up the idea of going through all 30k emails and picking up things that I might want to keep. I don't want to get rid of old emails of friends, family and other loved ones, so I'm looking for a solution to download the emails to my MacBook Pro (probably directly from Apple Mail) and store them in the hard disk in case I ever need to look for anything that might be of interest from the past, just feel nostalgic and want to go through old emails, or I happen to have the time and energy in the future to sort the emails out.
Is there any method you would recommend to export all emails and attachments and store them in a way that I can easily browse or search for keywords?