K-9 Mail Alternatives (January 2026)

K-9 Mail

K-9 Mail

https://k9mai.app/

K-9 Mail is an open source email client focused on making it easy to chew through large volumes of email

4.5/5

13+ reviews

Reviewed on:

G2
Capterra
1.
Mailspring - The best free email app
https://www.getmailsprin
.com/

Mailspring: The open-source, extensible email app for Mac, Linux, and Windows with open tracking, link click tracking, contacts enrichment data and more.

2.
BlueMail - The Best Email App for Windows, Mac, Linux, Android and iOS
https://bluemai
.me/

BlueMail is a modern, mobile and desktop, powerful Email management tool with a sleek design, unified inbox and support for all your accounts: IMAP, Exchange,POP3.

3.
RainLoop Webmail
https://www.rainloo
.net/

RainLoop Webmail - Simple, modern & fast web-based email client.

4.
Thunderbird — Free Your Inbox. — Thunderbird
https://www.thunderbir
.net/

Thunderbird is a free email application that’s easy to set up and customize - and it’s loaded with great features!

5.
The Power Email App - Postbox
https://www.postbox-in
.com/

Postbox is the power email app for busy professionals, like you.

6.
Sylpheed - 軽快で使いやすいオープンソースのメールソフト
https://sylpheed.sraos
.jp/

Sylpheed - Sylpheed はシンプル、軽量かつ高機能で使いやすい、無料のメールソフトです。Sylpheed は Windows から Linux まで様々なプラットフォームに対応しています。

7.
Spark Mail — Smart. Focused. Email.
https://sparkmailap
.com/

Spark helps you take your inbox under control. Instantly see what’s important and quickly clean up the rest.

8.
Mail-in-a-Box
https://mailinabo
.email/

Take back control of your email with this easy-to-deploy mail server in a box.

9.
TypeApp | Home
https://typeap
.com/

TypeApp - The best Android and iOS email app ever created for mobile devices. Fast, simple and easy, TypeApp is the best email app for Android and iOS