Airmail
Used by 8 peopleairmailapp.com ↗

“I run Airmail on Mac & iOS to unify all my inboxes and so I can read email in a native application.”
C J Silverio Interview, Software developer · via Uses This 
“I'm perpetually on the lookout for a really good desktop email client - currently I'm using Airmail, which isn't bad.”
Louisa Heinrich Interview, Designer, founder (Superhuman Limited) · via Uses This