Define great. ;-)
KMail has multiple issues, which are known for a very long time. It might work for some people, but for me Evolution and Thunderbird work 100% OOTB with all my email accounts, which is and has not been true with KMail, not even speaking about KMail corrupting local email storage etc.
If you look only at the comments under the linked article, multiple people expressed having problems with KMail…
IMHO this is a really big problem: Most of my life depends on my email client working correctly and w/o a hitch: Reminders for appointments, communication for all purposes, important emails etc. KMail really ‘earned’ its bad reputation in the last years, which I am not happy about.
Nice one, although I am sorry for your shitty experience with the employer. We should have a world wide open database about employers pulling this kind of shit!