Hey guys,
I was thinking about setting up my own mail server. Problem is my ISP will not let me have a static IP unless I upgrade to a Business class service which is just too expensive for home use. As a work around I use a DDNS service from Dlink, which is actually done via DYNDNS.com. So essentially I have mydomain.dlinkddns.com point to my Dynamic WAN IP, and it is all automatically managed by my router.

Is there a way I can have mymaildomain.com point to my mail server without it being a subdomain of my DDNS (mydomain.dlinkddns.com)? In other words I would like to have the email someone@mymaildomain.com and not have it be someone@mydomain.dlinkddns.com, or someone@mymaildomain.mydomain.dlinkddns.com or something like that. I know someone has done it, I just have never done it. Not quite sure what to google to find the answer myself either.

Can anyone point me in the right direction and give me a starting point to do my research?

Well there's nothing forcing any constraint on what domain names can be used on MX records. As long as you set the MX record on your "nice" domain to the ddns name then you'll be fine.

How can I set the MX record on "nice" domain?

that's up to you... where did you get the domain from? How does your DNS work for it? I've done things like by a domain from a registrar, £10 per year and then ask them to set the domains NS records to zoneedit.com and then use the free DNS services there to configure the other DNS records as I see fit.

I get all my domains from godaddy.com. From there I can specify any NS server I want. This is just new territory for me so I am trying to understand the basics before I dive head first into this. I think I understand what I am looking at and have a nice starting point. Thanks for your help.