K-9 Mail vs Thunderbird (2026): which should you pick?
As of Nov 13, 2026, Thunderbird grades higher than K-9 Mail: 3.2 against 2.8 out of 4.0.
Checked Oct 5, 2026 and Nov 13, 2026 · graded Oct 10, 2026 and Nov 13, 2026 by ToolGPA
Thunderbird grades higher on platforms. They get the same grade on value for money, the free plan, features and ease of use.
Price, platforms and features side by side. The table says where each price was read and when.
Thunderbird
Free, open-source email app for Windows, macOS, Linux and Android
Free
Which one is for you
Pick K-9 Mail if
- Fits if you read several mailboxes on one Android phone
- Works for people who want GPG and open-source code
Look elsewhere if
- Not for you if you use iPhone or a computer, as it is Android only
- Watch out: the site's banner says Thunderbird for Android is the future of K-9 Mail
- Skip it if you need a new address, since it is a client for existing mailboxes
- Tight if you want setup done for you, as you add your own account details
Pick Thunderbird if
- Fits if you want a free desktop email app with no ads in it
- Works for people who move between Windows, macOS and Linux and want the same app on each
Look elsewhere if
- Skip it if you're on an iPhone, as Thunderbird Mobile is listed for Android only
- Not for you if you want someone to call when it breaks, because support is community-based
- Too light for anyone who needs an email address as well, since it's a mail app, not a mailbox
- Watch out: Thundermail, the team's own hosting, is a separate paid beta behind a waitlist, $6 a month yearly
- Skip it if you read mail in a browser, as there's no web version
How we grade them
| 2.8GPAK-9 MailGood | 3.2GPAThunderbirdVery good | |
|---|---|---|
| Value for money | AFree to download under the Apache 2.0 licence, with no paid plans, and a donate link. | AIt's free, where the middle of this category is $8 a month. Every feature of the desktop and Android apps costs $0, with no ads and no paid tier, funded by voluntary donations. Thundermail, the team's own hosting service, is a separate paid subscription and still in beta. |
| Free plan and trial | AThe full app is free from Google Play, F-Droid, GitHub or Amazon. | AThe whole app is free on desktop and Android, with no cap and nothing held back for a paid plan, because there isn't one. The trade-off is support: it's community-based, and Thunderbird says donations don't buy individual technical help. |
| Features | BPush IMAP, GPG and PGP/MIME, a unified inbox, identities and message tools. The listing shows no gap in the core job of a mail client, though it provides no address of its own. | BSeveral accounts read separately or in a unified inbox, with calendar, contacts and tasks in the desktop app so scheduling needs no second program, add-ons to extend it, and OpenPGP on Android through OpenKeychain. Nothing in the listing points at a hole in the mail-client job. |
| Ease of use | CNo store rating on record. You add your accounts and server settings yourself. | CNo rating on record, and this is a settings-heavy old hand rather than a tidy modern app: accounts to add, panes and add-ons to arrange, and community forums if you get stuck. A QR code copies your desktop accounts to the Android app. |
| Platforms and integrations | DAndroid only: no iPhone, desktop or web version is listed. | BWindows, macOS and Linux on the desktop and Android on the phone, so computer and phone are covered and Linux people are included for once. No iPhone or iPad app is listed, there's no web version, and the only integration on record is OpenKeychain. |
| Best for | an open-source Android email client | free, open-source email on any desktop |
The GPA is the average of the five grades: an A is 4 points, an F is none. The full reasons are on each tool's page: K-9 Mail and Thunderbird. How we grade
Price against what you get
K-9 Mail has no paid plan and scores 2.0 out of 4 on features, ease of use and platforms. Thunderbird has no paid plan and scores 2.7.
Thunderbird scores higher for the same starting price. Of the other email apps on the chart, none scores higher than K-9 Mail for less, and none scores higher than Thunderbird for less.
Features, ease of use and platforms, averaged
What paid plans start at, a month (each step along is roughly double) →
- The best score at each price
- Has a free plan
- No free plan
Where they differ
- Thunderbird also covers tasks and calendar.
In commonFree planAndroidOpen sourceEmail client
At a glance
| K-9 Mail | Thunderbird | |
|---|---|---|
| Pricing | Free | Free |
| Starts at | Free | Free |
| Free plan | Free to download from Google Play, F-Droid, GitHub Releases or Amazon; no paid plans are listed. | The whole app is free on desktop and Android, with no ads and no paid tier. Development is funded by voluntary donations. |
| Free trial | None listed | None listed |
| macOS | ||
| Windows | ||
| Linux | ||
| Android | ||
| Made by | K-9 Mail | MZLA Technologies Corporation |
| Price read from | k9mail.app | thunderbird.net |
| Checked | Nov 13, 2026 | Oct 5, 2026 |
Worth knowing
K-9 Mail
- Android only; no iOS, desktop or web version is listed.
- The site's banner says Thunderbird for Android is available now and calls it the future of K-9 Mail.
- It is a client for existing mailboxes and does not provide an email address.
Thunderbird
- Thunderbird Mobile is listed for Android only, through Google Play and F-Droid. No iPhone or iPad app is listed.
- It is a mail client, not a mailbox: it connects to accounts hosted elsewhere. The team's own hosting service, Thundermail, is in beta behind a waitlist.
- Thundermail is a separate paid subscription. Its Early Bird Plan is shown at $6 per month, paid annually, with full launch expected in 2026.
- Support is community-based. Thunderbird states that donations do not buy individual technical support.
Key features
K-9 Mail
- Push IMAP
- The feature list names push IMAP support, so new messages can arrive without polling on servers that allow it.
- GPG and PGP/MIME
- The site lists GPG and PGP/MIME support for signing and encrypting messages.
- Unified inbox and identities
- A unified inbox, per-account notifications and multiple identities are listed, along with signatures and BCC to self.
- Message handling tools
- Listed tools include message flagging, keyboard shortcuts, attachment saving and emoji support.
- Several ways to install
- The download page offers the Play Store (with a beta channel), F-Droid, GitHub Releases and Amazon.
Thunderbird
- Unified inbox for several accounts
- Keep every email account in one app and read them separately or together in a unified inbox, on desktop and on Android.
- Calendar, contacts and tasks
- The desktop app manages appointments, contacts and tasks alongside email, so scheduling does not need a separate program.
- No ads or data mining
- Thunderbird says it does not sell ads in the inbox, collect personal data or train AI on private conversations. It is funded by user donations.
- Open source and extensible
- The code is published under the MPL 2.0 license for anyone to inspect, modify and share, and add-ons extend what the desktop app can do.
- OpenPGP encryption on Android
- Advanced users can send and receive encrypted mail with the OpenPGP standard by pairing Thunderbird Mobile with the free OpenKeychain app.
- Desktop-to-mobile setup
- Desktop users can move their account settings to the Android app by scanning a QR code shown in the desktop app.
Plans
K-9 Mail
Free$0
Open source under the Apache License 2.0; the site has a donate link.
Thunderbird
Free$0
Every feature of Thunderbird Desktop for Windows, macOS and Linux and of Thunderbird Mobile for Android.
Common questions
Which is cheaper, K-9 Mail or Thunderbird?
As of Nov 13, 2026, both K-9 Mail and Thunderbird are free to use.
Which has a free plan, K-9 Mail or Thunderbird?
As of Nov 13, 2026, both K-9 Mail and Thunderbird have a free plan.
Which platforms do K-9 Mail and Thunderbird run on?
As of Nov 13, 2026, only Thunderbird lists macOS, Windows and Linux apps. Both list an Android app. A platform missing from a listing is one its maker's pages did not mention.
More comparisons
How this page was made
- The verdict at the top follows a fixed rule. When both tools are in the same category and either is in our top three for it, the verdict follows that ranking: the higher-placed tool is our pick. The top three weigh who each tool suits as well as its grades, so a pick can go against the GPA. Otherwise the page does not pick one and says which grades higher: the higher GPA first; on a tie, the one with a free plan, then the one that starts cheaper in dollars a month, counted the same way for both; if they are still level, what the choice depends on.
- The grades are our own, from each tool’s review or report card. The GPA is their average.
- Prices, plans and platforms come from each tool’s listing. The table above says where each price was read and when.
- The differences and the answers to the questions are worked out from those listings.