When comparing Alpine vs kmail, the Slant community recommends kmail for most people. In the question“What are the best email clients for UNIX-like systems?” kmail is ranked 8th while Alpine is ranked 10th. The most important reason people chose kmail is:
Its the only graphical email client which is properly integrated into kde plasma.
Specs
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Pros
Pro Extremely user-friendly
Pro Can use the built-in text editor or can be integrated with another text editor
Alpine comes with pico, a lightweight text editor which can also be used as a standalone tool. It can also be integrated with vi, vim, emacs, etc... if the user prefers to do so.
Pro On-screen contextual help
Alpine has contextual help that can be displayed on-screen. Removing the need to consult the man pages every time you forget a command or how to do something inside it.
Pro Proper kde intergation
Its the only graphical email client which is properly integrated into kde plasma.
Pro Has system tray icon
Good integration with plasma 5
Pro Supports POP3 and IMAP mailboxes
Cons
Con Updates are not frequent
Alpine is not updated frequently. This means that new features, bug fixes or security updates come much later than in other email clients.
Con Buggy as of 2020
There are many bugs which are hard to track down in kmail, sometimes without any useful logs for troubleshooting. Sometimes the bugs are related to supportive applications like Akonadi, ect.
Con Poor UX
The user experience of kmail is extremely poor comparison to Thunderbird or evolution on Linux.
Con Buggy related kdepim applications
kmail by itself isn't the only application which is buggy, the many of the kdepim applications are buggy as of spring 2020.
Con No google support
You cant pass google 'Authentication' for the majority of the kdepim applications, The only support which works is via the kde 'online accounts' under 'system settings'. This only supports youtube and google hangouts integration.
Con Akonadi
Akonadi needs lot of ram