All domains are "email-enabled", all of them /can/ be used for email.

You just have to setup an email server (or buy 'email server' access from someone who sells the same) somewhere that handles email for the domains. And then point the MX records in DNS for the domains for which you want to receive email at the email servers that handle email for those domains.

Well if it's cheap you're looking for there is Purelymail: https://purelymail.com/

Since you're already with Namecheap, why not go with one of their email plans/addons?

All you have to do is add an MX record in the DNS and you've email-ified the domain.

I like the answer you have received, but more concretely:

I own a domain handled by NameCheap on which I send and receive email. Originally I were running my own email servers, but I quickly realised that was more work than it was worth in my case, so now email sent and received on my NameCheap domain gets handled by FastMail.

cloudflare now allows you to set up email aliases -- e.g., support@yournewdomain.com to yourpersonalemail@gmail.com -- but i think you have to register the domains with them or transfer the DNS to them.

...but yes, it would be nice if someone offered a non-price-gouge-y option for all the things you'd need to get dangerous.