

Different versions of the application are available that supports Windows, Mac, and Linux platforms. The best thing is that you can download, install, and use Mozilla Thunderbird for free under defined terms and conditions. If you use Thunderbird, there are a number of add-ons available that you can install and utilize to customize and enhance the emailing experience. It is a desktop-based application that gives complete control and extensive ownership over the email messages. Thunderbird, developed by Mozilla Corporation, is a free, open-source app that allows managing emails, chats, news feeds, and newsgroups quite efficiently. It helps convert MBOX email clients such as Thunderbird, Apple Mail, Entourage, etc. The app interface for K-9 Mail will match Thunderbird's desktop application to some extent, however, it will not have features like calendars and tasks for now.TIP: Want to try an alternate email client such as Microsoft Outlook to overcome performance or other issues in Mozilla Thunderbird? Need a quick solution to convert Thunderbird MBOX file to Outlook PST format, try using Stellar Converter for MBOX software. Other prospective features include better message organization through message filters and folders, as well as account setups through auto-configuration by Thunderbird. Thunderbird and K-9 Mail users will be allowed to sync email data from their existing accounts through Firefox Sync from summer 2023.

Furthermore, both cketti and Sipes have decided to keep the project open-source therefore, due to shared funding, any donations sent to K-9 Mail will also be used by Thunderbird.

While only for Android users right now, Mozilla has stated that support for iOS is being considered too. Now, K-9 Mail's maintainer Christian Ketterer, known as "cketti", has also announced that K-9 Mail will soon become Thunderbird. The project manager for Thunderbird, Ryan Lee Sipes, had recently publicized that this project was on its way. Mozilla Thunderbird has announced that it is collaborating with K-9 Mail to bring its email client to Android.
