I never use webmail so I can't answer.
There is a spam filter but I have not had to use it since it changed. It's located in the cPanel, not email. I never get spam, ever.
I believe that SPF and DKIM are there in cPanel, you can search that in the knowledgebase where the FAQ is.
Pretty sure the the cal/webDAV are there, I don't ever use those.
I personally prefer POP3 because IMAP always polls your devices if the client is open and that can drain resources and batteries. Plus I only have certain email address on certain devices. That's just me.
I have never had problems using Namecheap for email. It's been 11 years of excellent service. Also their customer service is speedy and smart. They have a pretty good reputation.
I had Hostgator for a few years before they were bought by EIG which is a shady craphole. Also stay away from GoDaddy.
I have over time looked into other web hosts, but nothing compared to what I was getting for the price or my needs. I also set up a family member because their ISP had such garbage email service.
I find that paying for my email and using my own domains are much better because I don't have to be subjected to ads or data harvesting. Plus I get whatever email address I want.