What do you use - instead of Xobni (R.I.P.), for instance, for better mail search/contact management: Nimble, Mailspring, eM, Mailbird, or something else?

Ideally, I would like to have a cross-platform mail/contacts/calendar client that is small/lean [like Mutt], robust/fast/responsive with a clean/simple UI [as Pine], with a great search [like GMail/Spotlight], good contact management [like Xobni], and controllable by the keyboard or mouse [like Emacs].

Should be able to connect to Exchange/MSFT O365 and IMAP, additional protocol support for RSS, XMPP and NNTP (USENET NEWS) would be considered a plus.