Fediverse

It's plenty possible. An address can be broken down like this.

Protocol (https://) subdomain (lemmy.) domain (socdojo) top-level-domain/TLD (com) path (/some/file/name/here)

https://lemmy.socdojo.com/some/file/name/here

You will typically register a domain name at whatever TLD you like (historically they where meant to be .com for commerce, .gov for government, etc but that's only really enforced for certain types like gov or org) and then you create subdomain from that to point to whatever services you put on the domain.

So you can have whatever you want on the same domain. There are some considerations where you might not want them attached, domain categorization services get a bit imprecise a lot of times and you might get caught up in some security filtering as a result.

Email specifically is a whole new dragon to tame, with things like spam and IP reputation lists, dmarc, dkim, SPF records and a bunch of other things. So be aware that it's probably one of the hardest services to do entirely on your own.