Proton Mail Bridge v3.21.0

Added

• BRIDGE-379: Mailbox pre-check on Bridge startup & conflict resolver for Bridge internal mailboxes.

Changed

• BRIDGE-376: Explicitly catch Gluon DB mailbox name conflicts and report them to Sentry.
• BRIDGE-373: Extend user mailbox conflict resolver logging & report sync errors to Sentry.
• BRIDGE-366: Kill switch support for IMAP IDLE.
• BRIDGE-363: Observability metric support for IMAP connections.

Fixed

• BRIDGE-377: Correct API label field usage on user label conflict resolver - update handler (event loop).
• BRIDGE-378: Fix incorrect field usage for system mailbox names.