> IMAP's main downside is that you have to trust your email provider to not lose your email. While certainly unlikely, it's not impossible. With OfflineIMAP, you can download your Mailboxes and make you own backups of your Maildir.

A professional mail host ('professional' as in 'someone that somehows makes money by hosting email') is way more unlikely to lose data than most of us are.

Making backup is great by the way, but for such task I'd strongly recommend the good old fetchmail or the newer (and better) fdm (https://github.com/ft/fdm). Both support imap(s). Both can save to either mailbox or maildir.

If you need a local copy, go for fdm and a local copy of your mailbox, plain and simple.