Cloudflare doesn’t provide SSL certificates which can be used for S/MIME neither email traffic if that’s the question? 
You can add them to your CF account.
Point to temporary IP address such as 192.0.2.1 and using Redirect Rules you can create a redirect to your primary domain, but only for Web HTTP(S) traffic.
For emails, you could leverage the Email Routing feature, to have an email alias such as [email protected], [email protected], [email protected] which then forwards every email which comes to this email address to your private or some “primary email” e.g. [email protected].
However, this product cannot be used to sent out emails as and in the name of [email protected], etc. to some received e.g. [email protected].
This product only forwards emails to your destination address.
Where would you like to install it?
For email service, or hosting, Website?
You can “host” a simple Website and assets via Cloudflare Pages and other combination of products such as D1 for database and Workers for even more things.
However, Cloudflare doesn’t offer a standard web hosting plans neither is a web hosting service as there are available in the market such as DigitalOcean, Hetzner, etc…
I am afraid you either have to decide if you:
- Need a web hosting for each of the domains to have different content available
- Need a email service for each of the domains
- Need both for each of the domain
It’s 2025 almost, nowadays SSL is mandatory I’d say and easy to get through Let’s Encrypt, SSL.com and other providers.
if you have a domain added to Cloudflare account, and any proxied DNS record such as A www for it, pointed to either temporary IP address such as 192.0.2.1 you do get a free SSL certificate which works only for Web HTTP(S) traffic, or connected and pointed to to some of the Cloudflare products such as mentioned Pages or Workers.