What features are on the roadmap?
You can email your own ideas, too!

Calendaring
The next major release brings Calendaring — day, month, and year views, drag-and-drop event editing, recurring events, and calendar invitations. Fully native on both iOS and Android.
Starting with JMAP and CalDAV, with MSGraph and Google Calendar to follow. Offline editing works out of the box.
Read more

MacOS
🚀 Mailtemi email app runs on macOS!
The goals for the macOS version are ambitious.
Full offline support, not just a cached subset of messages like in mobile versions. Copy or move messages between accounts.
Import and export messages in MBOX format.
There is still work to be done, but the progress so far is exciting.

Linux & Mobile
What started as a GTK test harness is starting to look suspiciously like an email app.
A Linux phone running a native GTK email client, syncing your Microsoft Outlook calendar — with JSCalendar as the bridge.
GTK runs on Windows too.
Other features in the roadmap
Push Notifications
Will be limited to JMAP, MSGraph, and GMail API, which offer this notification mechanisms.
IMAP cannot achieve push notifications without requiring access to the user's password, which is not acceptable and will not be supported.
OS Integrations
Deep integration with iOS and Android system APIs.
Contacts synced via a JMAP server like Stalwart or Fastmail become a single source of truth, surfaced natively through Apple's ContactProvider and Android's ContactsProvider.
Files stored on a JMAP server appear seamlessly in the OS file picker via Apple's FileProvider and Android's Storage Access Framework.
JMAP Files
Cloud file storage over JMAP, based on the JMAP File Storage extension draft.
Exposes files and folders as a structured hierarchy — a modern alternative to WebDAV-based file storage.
Move/Copy Emails Across Accounts
Move or copy emails between accounts, whether they use JMAP, IMAP, or MSGraph.
Unified Email & Contacts