I had been told that using Cloudflare CDN would decrease page load time, so I tried it over the weekend and change the DNS appropriately at the domain registrars, but now no emails are being received? Can anyone anyone here help on that please?
Also, when doing the settings for Cloudflare as above, is that effectively changing the hosting?
No, the host is the server where your site is placed. Changing the DNS records for your domain does not move the site, it would instead make your site unavailable for the domain name.
The public DNS service by Cloudfare (184.108.40.206) is meant to be used by your browser or router to translate domain names to IP numbers. Your domain to be found on the internet should be pointed to the IP number of the server your site is hosted at.
So I think there is a misunderstanding here:
Using a CDN is like using a proxy for external storage for files your site is loading so they should be cached and served through the CDN storage, so the CDN need to grab your domain:
The files are then pulled and cached by theCDN from your site to load faster in pages viewed at your site.
The advantage with a CDN is to be a cache-storage for mainly large files to make them faster to fetch when your site needs them loaded as content in its served pages.