I like Thunderbird, because I can get the code and look at it, as well as make my own tweeks. 

The #1 issue that infuriates me about some mail programs is how they want to "hide" the RFC-822 or IP address from me whilst I'm reading the message. NO. I want to see the RFC-822 address, and at times, I want to see the IP source address. With Mozilla, I can tweek it to display the info I want - which is "more information!" to make some judgements for myself about the provenance of a message.

Outlook is horrible. It's constantly seeking to make things "easier." I don't want "easier." I want more information. 

Office suite? I like LibreOffice, again because I can massage the source if I wish. These are probably not the answers that many users want to hear, because they don't sling C/C++ code, but those are my answers.

Oh, and while I run on a managed Windows 10 system at work, I run mostly OS X on my home machines (Macs). Why? Because I've been using Unix since 1982, and OS X looks like BSD Unix when I open a terminal window, which for me is like "going home." I've worked on more than a dozen systems, from VM/370 to CP/M and lots of stuff in between, but in Silicon Valley, I spent almost all my time on SunOS and BSD, using GNU software. So OS X is  like going back 25 years for me, and I don't have to think about things too hard there -  I've already paid my dues to learn Unix.