Email & Externally Hosted Domains

[#1]

Hi folks,
I tried a few searches about this but either there's nothing out there or I don't know the right jargon to get the appropriate information to appear, so apologies if this has been covered before.
I have a domain name registered via PlusNet that is currently pointing to the ccgi server. I have recently bought a dedicated server and would like to point the DNS records at the new machine's IP. I had some trouble setting up postfix etc on the new machine to deal with email, so rather than continue to spend any time on it I see no reason not to keep using PlusNet to send & receive email at that domain.
From my current understanding of DNS & MX records, this should be a possibility, no? If so, what's the best way to go about doing this? If not, any postfix experts out there?

[#2]

The two obvious ways which spring to mind are:
Register another related domain name and then change .htaccess in your existing site:
redirect 301 / http://www.newdomain.com/
(or the various other ways Apache offers to redirect using .htaccess, eg. Rewrite)
or
Change your existing PN-hosted DNS ‘A’ record:
www.yourdomain.com. ;  IN   A  1.2.3.4
where 1.2.3.4 is your new (local to you) website’s IP address
I guess you may need PN’s cooperation to do this as it points to a CCGI server. PN must continue to host the unqualified (i.e. yourdomain.com) domain name or your incoming email will bounce or blackhole. Whether having remotely pointing www A-records but locally (to PN) pointing MX records upsets PN's admin, I have no idea; it is, as I guess you know, the converse of what people with their own kit normally do (SMTP delivered email - which is supported by PN) !   

[#3]

That's interesting stuff, thanks! I think the best way forward is to carry on with setting up the email server and move the whole thing across, really.