Mu stores its metadata in the maildir. The index is there just for speed and can be regenerated from the maildir. Meanwhile notmuch - a similar tool - has support for message tagging. I wish at least one of them supported both features.

I use this as my daily driving for email and find it works great. I like that I can still use other apps to look at mail (my phone) and mu works still.

As someone who's very un-savvy when it comes to managing email servers and mailboxes: what is the unixy solution for moving a mailbox from one IMAP server to another? Ideally is there such a solution that doesn't require me to have ssh access to both of the servers?

Like - can I download and back up an entire mailbox with mu? And restore it to a different server? Or can I do that with some other tool? If I had ssh access to both servers, and they both used Maildir. could I do it with mu?

I know what Maildir is but I don't know how to determine if my IMAP server is using it, or something that looks like Maildir but isn't. My mail server runs dovecot and I'm pretty sure stores mail as Maildir, it looks like Maildir in the file system, but I wouldn't know how to positively verify that.

I know these are very random questions, just trying to figure out how to have more control of my mail...!

Good old mu, I use a combination of isync, mu, and mu4e for downloading, indexing, and reading/wrangling my mail. It works like a charm, though I did have to set mu4e-change-filenames-when-moving to avoid isync getting hung up on duplicate mail IDs.