eM Client was recommended to me by a Fruux.com employee (I have an account there) as having native support for all their DAV protocols. That was enough to convince me to try it, but there are so many other good things about it. A couple that are important to me:
- Incredibly flexible category system with unlimited color customization
- Ability to quickly and easily create and edit custom themes
As a visually impaired person, these features help me to quickly find and focus on the information I need with a minimum of eyestrain (and I keep track of LOTS of information for several different groups). That’s enough to be grateful for right there.
But wait - there’s more!
For some time, I’ve observed and participated in forum interactions between eM Client users and support personnel. My husband has been a support tech for many years, and I know what he has to put up with, and the amount of stress he’s under. I’ve seen some rather impolite people here directing negativity at various support people, and I have to say that the support people have behaved admirably, even in the face of repeated verbal assaults. I admit, I was a tiny bit snarky myself, for which I apologize - shame on me 
It was this professional behavior that finally convinced me that eM Client is well worth the price of the lifetime license. eM Client already does the things I really need, and knowing that it has such excellent support has made my decision final - I’m ditching Outlook and Thunderbird for good.
Special thanks to:
- George Wilson, who gathered and posted links to various user-created themes (https://forum.emclient.com/emclient/topics/custom_em_client_themes), which helped me A LOT.
- John Galis, for bumping the thread and keeping it active.
- Paul McGregor, for being a nice guy and responding to my questions about rules (sorry for the snark).
After years of frustration, I’m glad to have found a great piece of software with equally great people to support it. Nice going, you guys