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Proton Bridge

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Velocity2.5

Encrypted email bridge connecting Proton Mail to desktop email clients

proton.me/mail/bridge ↗

Proton's IMAP gateway is in deep maintenance, hardening fixes only.

imap-smtpencrypted-mailregression-fixescertificate-validationfeature-flagsmacos-support
◆Current state
Proton Bridge — the local IMAP/SMTP gateway that lets standard mail clients talk to Proton's encrypted backend — has settled into a hardening-and-fix rhythm. Recent releases are dominated by certificate validation fixes, mailbox conflict resolution, label/unlabel endpoint regressions, and OS compatibility work (macOS 26). No directionally new capabilities have shipped in over a year.
◆Where it's heading
Cadence is steady at roughly one minor or patch release per month, structured around mistakes that bit users: a Drafts-to-Trash deletion regression in 3.23.x, the unlabel endpoint reversion in 3.24.1. The team is reacting by adding feature flags so risky logic can be toggled post-release, and by expanding Sentry instrumentation around mailbox sync and auto-update failures.
◆Prediction
Expect more incremental protocol hardening — mailbox conflict cases, IMAP IDLE behaviour, certificate handling — gated behind feature flags. No directional product change is signaled in the changelog.

◆Recent moves

  1. 24d ago

    Bridge 3.24.2: Debian Bullseye Go base bump

    Pure base-image refresh: the Go build base moves to Debian Bullseye. No user-visible change. Fits the trajectory of quiet hardening.

    View source ↗
  2. 1mo ago

    Bridge 3.24.1: restore old unlabel endpoint behind feature flag

    Reverts the unlabel endpoint behaviour from 3.24.0 behind a feature flag after it broke something for users. A pattern the team now applies consistently — risky changes ship with a kill-switch.

    View source ↗
  3. 1mo ago

    Bridge 3.24.0: IMAP connection limiting, error mapping, RSA escape valve

    Substantive 3.24.0: IMAP connection limiting via Gluon, an error-mapping package to flatten error chains, a SplitHeaderBody perf variant, and a GODEBUG escape valve for sub-1024-bit RSA keys. Mostly correctness and edge-case scaffolding rather than new capability.

    View source ↗
  4. 1mo ago

    Bridge 3.23.1: fix Drafts-to-Trash deletion regression

    Hot-fix restoring pre-3.23 RemoveFromMailbox semantics so that Drafts moved to Trash are no longer permanently deleted. A user-visible data-loss bug exactly of the kind the feature-flag discipline was meant to avoid.

    View source ↗
  5. 2mo ago

    Bridge 3.21.2: tighten certificate pin validation to leaf certs

    Certificate pin validation is now scoped to leaf certificates only, fixing a chain-validation bug. Security-relevant correctness fix on a mature product.

    View source ↗
  6. 2mo ago

    Bridge 3.23.0: macOS 26 icon, CLI version, offline spinner

    Adds macOS 26 icon customization support, a CLI version readout, and an offline-state UI spinner. Small UX polish across desktop platforms; no protocol change.

    View source ↗