CNAMEs and managing DNS for a subdomain of someone else's domain

Hi folks,

I'd appreciate clarification on how CNAME works. Let's say my web server is listening for clubsite.ratsta.com. A completely separate organisation (domain.org) then creates a CNAME on their DNS that points myruralclub.domain.org to clubsite.ratsta.com. Will visitors to myruralclub.domain.org arrive at my server? Will they always see myruralclub.domain.org?

From reading Cloudflare's page on CNAMEs, I think that's what will happen, but I'd appreciate confirmation.

If so, that's great!

Second question, I'd like to set up shared mailboxes like president@myruralgroup.domain.org if I can. It seems that's as simple as getting the domain.org people to create a new MX record for the subdomain that points to the CNAME (and I need to set up my own mail server of course). Does that sound right?

---

The Big Picture

I'm a member of a tiny rural club that is a regional chapter of a state-wide group. They have their own web presence of course, at domain.org. I would like to create a web presence for our local group. I could just register my own domain but I think a far better option would be for us to use a subdomain of theirs. e.g. myruralgroup.domain.org.

I'd like to self-host the site. I have all the infrastructure except a static IP address. Long story short, I have no idea if the HQ even have an IT team and given the non-technical nature of the organisation, I expect that asking about integrating a DDNS tool with their infrastructure is likely to result in them never returning my calls :)

I'd like a solution where I can effectively update the IP address myself, should I need to. My searching suggests that we can't split the myruralgroup.domain.org subdomain. The only other thing I've thought of is CNAMEs but thus far I've only used them to create aliases within my own domain so I don't really understand how they work and would appreciate some advice.

Thanks!

https://redd.it/1x79xc4
@r_SelfHosted