I file emails from several email addresses into folders on iCloud. So I already have folders on iCloud for recent stuff of the last two years (eg. 2023+2024 – I hold a previous year back online there). I have the 2TB plan so storage not an issue along with Documents/Desktop iCloud Drive usage.
Previous years of folder archives at the moment are stored on one of my Macs ‘On My Mac’ areas in Mail.app, as I look for a decent solution.
Remember one important idea here is to get archives out of search in your Mail clients entirely (generally ‘out of mind’), so dragging them back onto any cloud IMAP email account doesn’t solve that issue. But somewhat ironically, I also want to be able to quickly go back and be able to look at these archives separately, without having to re-import them into a mail client each time to do so, especially if attachments are on emails (yes I save attachments on receipt of emails outside mail.app already, but you might still have to see them in the archive later as well, and doing that is difficult without importing the emails with attachments back into an email client).
Yes, I know this likely sounds like having my cake and eating it, lol!
It’s a shame Apple don’t offer the same kind of solutions MS offer for Exchange users, who have simple archive inside Outlook.app itself, provided it’s setup. See the options 2+3 here (mainly option 3):
