# emersion/hydroxide

A third-party, open-source ProtonMail CardDAV, IMAP and SMTP bridge

Repository: https://github.com/emersion/hydroxide
Canonical: https://ross.abutalabs.com/products/hydroxide
Homepage: https://codeberg.org/emersion/hydroxide
Language: Go
License: MIT
License Family: permissive
Topics: carddav, protonmail, smtp, imap, mail
Archived: true
Last push: 2026-08-02T09:30:39+00:00

## Health v2 (maintenance only)
Score: 10/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 95, release rhythm 59, longevity 100
- inputs: {"age_days": 3299, "days_push": 31, "days_rel": 115, "gap_med": 147.0, "n_releases_24m": 3}
- flags: archived
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2176, forks 183 (observed 2026-08-28T04:06:22.210519+00:00)

## What it is
Hydroxide is a third-party, open-source ProtonMail bridge written in Go that translates standard protocols (IMAP, SMTP, CardDAV) into ProtonMail API requests. It runs as a headless CLI server designed for power users who want to use standard email clients or git-send-email with ProtonMail.

## Use cases
- access ProtonMail from a standard email client via IMAP
- send email through ProtonMail using SMTP from any mail client
- sync ProtonMail contacts with CardDAV clients like Evolution or DAVdroid
- use git-send-email with a ProtonMail account
- run a ProtonMail bridge on a headless server without a GUI
- self-host an open-source alternative to the official ProtonMail bridge

## When to choose
- you want a fully open-source, GUI-free ProtonMail bridge for a server or headless environment
- you need standard-protocol access (IMAP/SMTP/CardDAV) to ProtonMail for clients like Evolution, DAVdroid, or git-send-email
- you prefer a lightweight CLI tool over the official proprietary bridge

## When to avoid
- you need polished, fully-supported IMAP support - it is explicitly work-in-progress with unencrypted local connections only
- you want a graphical desktop app or official vendor support
- you need Microsoft Outlook compatibility - the project explicitly does not target it
- you expect actively maintained software - it is casually maintained and has migrated to Codeberg

## Facets
- artifact type: service
- maturity: maintenance
- function: email, http-server, security, cryptography
- domain: email, privacy, self-hosted, developer-tools
- platform: windows, cli, self-hosted, go
- tags: protonmail, imap, smtp, carddav, bridge, headless, git-send-email, linux, macos

## Member repositories
- emersion/hydroxide (main) score 10

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:22.210519+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T02:48:52.523617+00:00, confidence not recorded.
  - readme: https://github.com/emersion/hydroxide (fetched 2026-08-28T04:06:22.210519+00:00, sha e71a52583058)
  - homepage: https://codeberg.org/emersion/hydroxide (fetched 2026-08-29T10:29:31.273800+00:00, sha ed730dc2da50)
  - site_page: https://docs.codeberg.org/getting-started/what-is-codeberg (fetched 2026-08-29T10:29:31.282729+00:00, sha fe3047f34c81)
  - site_page: https://docs.codeberg.org/getting-started/faq (fetched 2026-08-29T10:29:31.284989+00:00, sha 7ffd1ab1d66b)
  - site_page: https://docs.codeberg.org (fetched 2026-08-29T10:29:31.289067+00:00, sha 3c642f9d47c9)
  - site_page: https://codeberg.org/emersion/hydroxide/releases (fetched 2026-08-29T10:29:31.287161+00:00, sha e291b0ad99ad)
- Data as of 2026-08-30T08:39:29.467469+00:00.