Thunderbird is a free, open source, cross-platform e-mail, news and instant messaging client. The project strategy is modeled after Mozilla Firefox.
Thunderbird vs Evolution opinions
TB is also open source but not very easy to configure MS office365/exchange accounts
Clearer & more concise GUI
Boost your productivity and send better email with Mailspring, a beautiful, fast email client for Mac, Windows, and Linux. Mailspring is free to use and an optional pro version adds read receipts, send later, reminders and more.
Geary is an email application built around conversations, for the GNOME 3 desktop.
Geary vs Evolution opinions
The comment that developers have "retired Evolution" is false. Both seem to be actively developed.
Geary only supports email, as opposed to Evolution, which is a full suite (email, calendar, contacts)
Evolution Developers have retired Evolution; and moved to Geary.
Claws Mail is an email client (and news reader), based on GTK+, featuring
Quick response Graceful, and sophisticated interface Easy configuration, intuitive operation Abundant features Extensibility Robustness and stability.
Claws Mail vs Evolution opinions
It's just an E-Mail client , doesn't have any calendar and CalDav support.
Mutt is a small but very powerful text-based mail client for Unix operating systems. Some of its features are: color support, message threading, MIME support (including RFC2047 support for encoded headers), PGP/MIME (RFC2015), various features to support mailing lists, including...
Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features. The development of Mailpile is funded by a large community of backers and all code related to the project is and will be released under an OSI approved Free Software license.Discontinued
1.0.0 Release Candidate 6 from 2019 is the last version on GitHub (https://github.com/mailpile/Mailpile/releases). Possibly the development has been stopped.
KMail is the email component of Kontact, the integrated personal information manager of KDE. Kontact is a personal information manager and groupware software suite for KDE. It supports calendars, contacts, notes, to-do lists, news, and email.
BlueMail is a modern, mobile first, powerful Email management tool with a sleek design, unified inbox and support for all your accounts: IMAP,Exchange,POP3.
Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).
Sylpheed vs Evolution opinions
It is just a simple E-Mail client and doesn't have any Calendar support.