Betterbird is a fine-tuned version of Mozilla Thunderbird, Thunderbird on steroids, if you will.

Betterbird is better than Thunderbird in three ways: It contains new features exclusive to Betterbird, it contains bug fixes exclusive to Betterbird and it contains fixes that Thunderbird may ship at a later stage.

K-9 Mail is an open source email client that works with basically every email provider.

Meet Thunderbird, the email, calendar, and contacts app that maximizes your freedoms.

Access all your messages, calendars, and contacts in one fast app. Filter and organize the way you like. Manage all accounts separately or in a unified inbox. Thunderbird simply makes your life simpler.