Open-source Email Outbound tools

The best open-source Email Outbound tools, curated: 9 in the registry, including gmailctl, google-api-python-client (Docs/Drive), himalaya. Every tool is open-source; each entry lists license, self-hostability, and links.

9 tools · ← all categories · JSON

• gmailctl — tool, 2026-09-03
  ~2200 stars; complements google-api-python-client; Uses official Gmail API to sync filters. Auth via OAuth2. Diff-before-apply. No ToS risk.
• google-api-python-client (Docs/Drive) — tool, 2026-09-03
  ~8900 stars; complements gmailctl; Official Google API client (maintenance mode but supported). Gmail API auth via OAuth2. No ToS risk; per-user API quotas.
• himalaya — tool, 2026-09-03
  ~7000 stars; complements imap_tools, isync/mbsync; Open protocols (IMAP/SMTP/JMAP) plus Gmail REST and Graph backends. Auth: password/OAuth2/XOAUTH2. No ToS risk.
• imap_tools — tool, 2026-09-03
  ~836 stars; complements himalaya; Open IMAP protocol (over imaplib). Auth via credentials/app-password/OAuth. No ToS risk.
• mail-parser (SpamScope) — tool, 2026-09-03
  ~452 stars; complements email-reply-parser; Pure parsing library (no network/auth). RFC-compliant, Outlook .msg support, defect detection. No ToS risk.
• msgraph-sdk-python (Microsoft Graph) — tool, 2026-09-03
  ~624 stars; complements python-o365, exchangelib; Official Microsoft Graph v1.0 Python SDK. Auth via MSAL OAuth2 (app/delegated). No ToS risk.
• proton-bridge — tool, 2026-09-03
  ~1500 stars; complements hydroxide; Official Proton Mail Bridge; exposes local IMAP/SMTP for standard clients. Auth via Proton login + keychain. Requires paid Proton plan. No ToS risk (sanctioned).
• python-o365 — tool, 2026-09-03
  ~1900 stars; complements msgraph-sdk-python, exchangelib; Ergonomic wrapper over Microsoft Graph. Auth via OAuth2. No ToS risk; friendlier than raw Graph SDK.
• Cold Outbound Skills — tool, 2026-09-03
  Thirty open-source Claude Code skills covering the cold-email motion end to end — lead sourcing, copywriting, deliverability/infrastructure setup and campaign operations — packaged by growth operator Eric Nowoslawski.