# Alternatives to K-9 Mail Open source Android mail, now Thunderbird Mobile. K-9 Mail ranks #21 of 22 in Email clients, with an Alt Score of 47. It is licensed under Apache-2.0, free and available on Android. 5 of 11 checklist rows are verified against a public source. Source: https://altcatalog.com/alternatives/k-9-mail/ Category: Email clients ## Overview - **Who it's for**: Android users who want a full-featured, open-source email client for managing IMAP/POP3 accounts, especially those handling high volumes of email across multiple accounts. - **What you get**: Push IMAP for real-time mail delivery, a unified inbox across multiple accounts and identities, and OpenPGP/S-MIME encryption support. It offers per-account notification controls, message flagging, keyboard shortcuts, and light/dark themes. As an open-source project (the basis for Thunderbird for Android), its source is fully auditable. - **How it works**: Install the app from Google Play, F-Droid, or GitHub, then add one or more email accounts via IMAP or POP3 with the setup wizard. Once configured, messages sync in the background and appear in a unified inbox, where you can read, flag, encrypt, and organize mail across all connected accounts. ## Profile - **License**: Apache-2.0 (verified 2026-07-12) - **Pricing model**: Free (verified 2026-07-12) - **Starts at**: ? - **Platforms**: Android - **Status**: active (verified 2026-07-12) ## Ranked alternatives | # | App | Alt Score | Licence | Platforms | |---|-----|-----------|---------|-----------| | 1 | [eM Client](https://altcatalog.com/alternatives/em-client.md) | 96 | Proprietary | Windows, macOS, iOS, Android | | 2 | [BlueMail](https://altcatalog.com/alternatives/bluemail.md) | 92 | Proprietary | Windows, macOS, Linux, iOS | | 3 | [Canary Mail](https://altcatalog.com/alternatives/canary-mail.md) | 92 | Proprietary | Windows, macOS, iOS, Android | | 4 | [The Bat!](https://altcatalog.com/alternatives/the-bat.md) | 92 | Proprietary | Windows | | 5 | [Apple Mail](https://altcatalog.com/alternatives/apple-mail.md) | 87 | Proprietary | macOS, iOS | | 6 | [FairEmail](https://altcatalog.com/alternatives/fairemail.md) | 87 | GPL-3.0 | Android | | 7 | [Mailbird](https://altcatalog.com/alternatives/mailbird.md) | 87 | Proprietary | Windows, macOS | | 8 | [Evolution](https://altcatalog.com/alternatives/evolution.md) | 84 | LGPL-2.1 | Linux | | 9 | [Mailspring](https://altcatalog.com/alternatives/mailspring.md) | 84 | GPL-3.0 | Windows, macOS, Linux | | 10 | [Missive](https://altcatalog.com/alternatives/missive.md) | 84 | Proprietary | Web, Windows, macOS, iOS | | 11 | [Outlook](https://altcatalog.com/alternatives/outlook.md) | 84 | Proprietary | Windows, macOS, iOS, Android | | 12 | [Thunderbird](https://altcatalog.com/alternatives/thunderbird.md) | 76 | MPL-2.0 | Windows, macOS, Linux | | 13 | [Spark](https://altcatalog.com/alternatives/spark.md) | 71 | Proprietary | Windows, macOS, iOS, Android | | 14 | [NeoMutt](https://altcatalog.com/alternatives/neomutt.md) | 68 | GPL-2.0 | Linux, macOS | | 15 | [Shortwave](https://altcatalog.com/alternatives/shortwave.md) | 68 | Proprietary | Web, macOS, Windows, iOS | | 16 | [Postbox](https://altcatalog.com/alternatives/postbox.md) | 63 | Proprietary | macOS, Windows | | 17 | [Mimestream](https://altcatalog.com/alternatives/mimestream.md) | 60 | Proprietary | macOS | | 18 | [Aqua Mail](https://altcatalog.com/alternatives/aqua-mail.md) | 55 | Proprietary | Android | | 19 | [Superhuman](https://altcatalog.com/alternatives/superhuman.md) | 55 | Proprietary | Windows, macOS, iOS, Android | | 20 | [Geary](https://altcatalog.com/alternatives/geary.md) | 50 | LGPL-2.1-or-later | Linux | | 21 | [aerc](https://altcatalog.com/alternatives/aerc.md) | 42 | MIT | Linux, macOS | Alt Score = Verified coverage (90%) + Visibility (10%). See https://altcatalog.com/how-alt-score-works/ ## Feature comparison Legend: Yes / No / Partial / ? (not verified). | Email clients checklist | K-9 Mail | eM Client | BlueMail | Canary Mail | The Bat! | Apple Mail | |---|---|---|---|---|---|---| | Pricing model | Free | Freemium | Freemium | Freemium | One-time | Free | | Starts at | ? | €39.95/year | ? | $3/month | €47.95 one-time (Home Edition) | ? | | License | Apache-2.0 | Proprietary | Proprietary | Proprietary | Proprietary | Proprietary | | Platforms | Android | Windows, macOS, iOS, Android | Windows, macOS, Linux, iOS, Android, Web | Windows, macOS, iOS, Android | Windows | macOS, iOS | | Protocols (IMAP / POP3 / JMAP / Exchange) | Yes | Yes | Yes | Partial | Yes | Yes | | Unified inbox | Yes | Yes | Yes | Yes | Yes | Yes | | Snooze & send later | ? | Yes | Yes | Yes | Partial | Yes | | Tracking pixel blocking | ? | Yes | Yes | Yes | Yes | Yes | | PGP / encryption support | Yes | Yes | Yes | Yes | Yes | Partial | | Conversation view | Partial | Yes | Yes | Yes | Yes | Yes | | Offline mode | ? | Yes | Yes | Yes | Yes | Yes | | Rules & filters (local) | ? | Yes | Partial | Yes | Yes | Yes | | Calendar integrated | ? | Yes | Yes | Yes | Yes | Partial | | Multiple identities/aliases | Yes | Yes | Yes | Yes | Yes | Yes | | Keyboard-first shortcuts | ? | Partial | Partial | Partial | Partial | Partial | ## Sources Sources for K-9 Mail. Each alternative is sourced on its own page. - **Pricing model**: Free — (verified 2026-07-12) - Quote: “K-9 Mail is a 100% open source, privacy focused email client for Android” - **Platforms**: Android — (verified 2026-07-12) - Quote: “Outlook, Yahoo, Hotmail, iCloud, Office/ Outlook 365, Exchange, AOL, Gmail, and IMAP* mail accounts on your Android device.” - **Status**: active — (verified 2026-07-12) - Quote: “Built on open-source technology and supported by a dedicated team of developers alongside a global community of volunteers, Thunderbird never treats your private data as a product.” - **License**: Apache-2.0 — (verified 2026-07-12) - Quote: “Apache License” - **Protocols (IMAP / POP3 / JMAP / Exchange)**: Yes — (verified 2026-07-12) - Quote: “Thunderbird works with IMAP and POP3 protocols, supporting a wide range of email providers, including Gmail, Outlook, Yahoo Mail, iCloud, and more.” - **Unified inbox**: Yes — (verified 2026-07-12) - Quote: “By default, K-9 Mail combines the messages from your accounts into a single view called the Unified Inbox.” - **PGP / encryption support**: Yes — (verified 2026-07-12) - Quote: “K-9 Mail does not have built-in encryption capabilities. Instead, it uses an external Android application called OpenKeychain.” - **Conversation view**: Partial — (verified 2026-07-12) - Quote: “Please note that this is not the same as the conversation view you might know from e.g. Gmail.” - **Multiple identities/aliases**: Yes — (verified 2026-07-12) - Quote: “Here you can set up alternative identities consisting of name, email address, _Reply-to_ address, and signature.” --- Ranked by verified data, never by who paid. https://altcatalog.com/trust/