Thanks for the suggestions Till.
As you mentioned, sites like Hotmail won't accept email from dynamic dns sites, and that is why I was hoping to use my regular domain as a MX forwarder (internally on server). So, lets review what I have...I'll use different names here to clear up the example.
I have 2 sites with proper, static FQDN names, aaa.com and bbb.com. aaa.com also has a reverse-arp defined in my hosts's DNS server. They both have MX records registered, pointing to one IP address, 216.xxx.yyy.18. I also have 2 dyndns sites, ccc.com and ddd.com, which I would like to forward mail to if it is possible, and also have all 4 sites send mail.
So, if I register mail.aaa.com and mail.bbb.com as my MX's in my registrar's DNS records, can I use one of those to relay mail to my site's ccc.com and ddd.com websites/mail users? Can I specify mail.aaa.com as the "generic" MX under ispconfig, and have it relay all emails to the 4 sites on my machine?
That's why I asked about what IP/name I should used for the "Site" management boxes, and then the qustion would be, how would I configure the www.aaa.com
site in ispconfig as a virtual site as well to use the "Overall Site" MX relay?
Hope that makes it clearer. There must be people out there that run a mix of dyndns and registered DNS sites on one server...and have email working...
As for "all libraries are specified"... in the ISPConfig "Install Instructions", which I call a "howto", there is a comment: "Important: Be sure to have installed gcc, flex....You also need to install the MySQL header files which normally come in a package called mysql-devel, mysql-dev, libmysql-devel or something similar." "Something similar"?? That tells me nothing. The 3 mentioned above did not exist when I searched for them (maybe I did miss something there...). It was those libraries that I was missing, and this comment was so generic, I had to search google to find the compile error and a quoted text of what to install with a sample apt-get. It would be nice if you included a specific library install command at this point, I was left guessing for an hour of so to find a solution...