parked / add on domains

[carperman]

Hello, can anyone point me in direction of info on parked and addon domains, i am still a little confused how these can be used in real life; ie.

I have a site which sells emaill account on hundred of domains, some of the domain are repeats of themselves

gooddomain.com
good-domain.com

plus other top level types . net etc


Currently i have each domain with own account and a catchall all account for sold email accounts.


These setup account alos have a search engine friendly home page to help increase search engine exposure for main site.


Can/should i have just one account per domain on which others are addons:

gooddomain.com
with following as addons
good-domain.com
gooddomain.net


each have own catchall pop account.


How will this affect search engine exposure?

many thanks