Be Excellent To Each Other

If I have a domain at, for example, imreallygreat.co.uk - I shouldn't have to go through a Domain Registrar to set up itoldyou.imreallygreat.co.uk should I? And I should be able to send email to ferchristssake@itoldyou.imreallygreat.co.uk and ferchristssake@imreallygreat.co.uk because they are two different email addresses without a lot of faffing?

to do the itoldyou.imreallygreat.co.uk you need to have access to the DNS settings. 123-reg any many others let you do it through a control panel, and it's fairly easy. You'll also have to set this up on your webserver as well.

As for the email, again it depends on what access they give you the mail server settings.

I'm speaking genrically, as opposed to a specific ISP.

Its actually concerning a .ac.uk domain.

I can confirm I did lots of that kind of thing when I ran a .ac.uk domain. We had our own DNS server, obviously.

They'll be a name/dns server that hosts your info. When someone wants plissken.ac.uk, they'll talk to that server and say "what ip is it, plz?". If someone wnats what.the.hell.plissken.ac.uk, they'll talk to the same server, as it's the most they know about. That server can either redirect them to another dns server, who knows where to find hell.plissken.ac.uk, or the server itself will know (because you told it).

Either way; it's kinda "free". As long as you can change the dns entries somehow, you can add as many silly sub domains as you like.