When comparing kmail vs Mu4e, the Slant community recommends Mu4e for most people. In the question“What are the best Linux email clients?” Mu4e is ranked 7th while kmail is ranked 11th. The most important reason people chose Mu4e is:
The UI is designed to allow for quick keystrokes to get around and is pretty clean. Header View: !(http://www.djcbsoftware.nl/code/mu/mu4e-2.png) Message View: !(http://www.djcbsoftware.nl/code/mu/mu4e-3.png)
Ranked in these QuestionsQuestion Ranking
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
Heavy actions never block emacs, unlike most other emacs email clients.
Pro Fully Search Based
Mu4e has no folders or other organizational tools, rather it relies on very fast search queries to help you find your mail.
Pro Can write rich text emails
Using the (beta) org mode, Mu4e can compose fully rich text emails.
Pro Built-in Autocomplete
Doesn't require you to import address books for autocomplete, learns from your emails just like Gmail.
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 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 Poor UX
The user experience of kmail is extremely poor comparison to Thunderbird or evolution on Linux.
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.
Akonadi needs lot of ram