[gkmcd]

I have a local maildir[1] account in Evolution. Each of my (IMAP) mail accounts is set so the "archive" command moves the message to a folder under the maildir account (if you're using Evolution, this can be configured under "Defaults" in the account properties for each IMAP account). Anything worth keeping from any of my IMAP mail accounts is archived to the local maildir, everything else is deleted.

The local maildir account is searchable like any other mailbox (I have about 10,000 messages going back to 2003). Syncthing[2] is configured to sync the maildir directory for backup and sync.

[1]https://en.wikipedia.org/wiki/Maildir

[2]https://syncthing.net/