Mailspring

## 1.26.0 (10/1/2026)

This is a major sync reliability release - The sync engine now tracks every folder a message lives in, rather than forcing each message into a single folder. This permanently fixes mail "flickering" between folders or disappearing from the Inbox when the same message exists in two places — a long-standing issue for iCloud users, self-addressed mail that lands in both Inbox and Sent, Exchange's duplicate Sent copies, and ProtonMail labels. (#2891) This refactor was enabled by a huge new suite of automated mailsync tests that run against real Dovecot, Cyrus in Docker and fake problematic IMAP servers.

Features:

- Folder and unread counts left wrong by previous versions are repaired automatically on upgrade. Thanks @dansleboby!
- Calendars now refresh every 15 minutes instead of every 45, so invitations accepted on another device or meetings moved by the organizer show up sooner. Contacts sync slightly less often to conserve Google API quota. Thanks @brhellman!
- After an event is saved or deleted, Mailspring re-reads the calendar from the server so the event reflects what the server actually stored. (#2915) Thanks @brhellman!
- Calendars deleted or u