It has never let me down. However, I like Kmail a lot and may
switch. It has some features lacking in Thunderbird.

I think that people want something that has a built in PIM like Outlook and are
drawn to Evolution for that reason. You can get some features in Thunderbird
with Calendar Add-on. I am not into time management as I am retired and my time
was managed all my work life. My rebellion in old age. Kmail integrates with
Kontact and

There is Spicebird which is still in beta for the more adventurous in need of a
bit more than email. It works with Google calendar.