Oh I've been waiting for this. https://blog.fastmail.com/2017/06/26/dark-theme/

Good time to recommend FastMail again, I use it for all my mail, personal and business. 50$/year, 2FA and no ads of course, good spam filter, custom domains and aliases (including wildcards), SMTP/IMAP with unique app passwords, good Android app.

It's a serious mail service and much more reliable and time saving than managing your own mail servers.