Thanks, keeping this as a reference — I'm trying to find some time to try mu4e. I used Gnus for many years, then switched to Apple Mail.app, but with the gradual decline of MacOS (and Mail.app) I'm looking to switch back.

I remember the two main reasons I switched from Gnus: 1) there was no good reliable search, 2) I couldn't drag&drop attachments into E-mails and back so I was spending a lot of time pointing to files. I hope both things have improved since then.