If you're looking for a more traditional email client, I'd recommend MailMate[1]. It's a no-fuss email client designed for power user (GPG support, Markdown support, advanced filtering, text-only mode, etc.) I've been using it for half a year with Fastmail (personal) and Gmail (work) and pretty happy with it.
The author also maintains a blog[2] where he post quirks about several IMAP implementations. For example, Yahoo IMAP[3] or Gmail labels[4]. The app itself also handled all these edge cases very well.
[1]: https://freron.com
[3]: https://blog.freron.com/2017/slow-descent-into-madness-yahoo...
[4]: https://blog.freron.com/2013/mavericks-gmail-apple-mail-and-...