Keryx Mail
An original Android client for JMAP, written from scratch: mail, contacts, calendar, and tasks in one modern app.
Why JMAP?
IMAP was designed when a mailbox lived on one machine and you visited it. JMAP was designed for phones: one connection, real push, and a single round trip where IMAP needs a dozen.
It carries contacts, calendars, and tasks over the same protocol, which is why Keryx can be one app instead of four that happen to share an icon.
Not on JMAP yet? Keryx also speaks IMAP, SMTP, CalDAV, and CardDAV in full, so it works against any standard server today. No Google, ever.
Pre-release. Keryx is used daily as my own mail app, against a Stalwart JMAP server. Screenshots are coming as the interface settles.
Mail, calendar, contacts, tasks — one herald.
Keryx is the ancient Greek word for herald — the trusted messenger who carried word between cities and delivered it intact. That's the whole job here: mail, calendar, contacts, and tasks carried between you and your server, delivered faithfully, with no one else in the middle.