New Install working but issues with mail

I orginally posted this in the general topic but got no responses and couldn't figure out how to move it to this group...

I currently have IPSconfig installed and working but have some questions as to if I have things set up in the best way.

I have cable internet access to my home with 5 useable ips.

The cable internet access comes into a cable modem/router (i have no access to this router it is the cable companies). The router has 5 ethernet ports on it. I have one cable going from the modem/router to my Linksy box and then I have my internal home network (192.x.x.x) work just fine.

The ISPConfig server is actually on a Microsoft Virtual server with two nics. THe ISPConfig/CentOS server is assigned a nic that is plugged directly into the Cable modem to get one of the 5 usable ips. My question is do i need some sort of additional Firewall or is the firewall that ISPConfig has sufficient?

Additional Questions
--On step two of CentOS 4.6 Server Setup: LAMP, Email, DNS, FTP, ISPConfig (a.k.a. The Perfect Server) if my current set up is correct i am assuming i need to apply my external IP vs. the way it is documented in the set up.

(# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 localhost.localdomain localhost
192.168.0.100 server1.example.com server1)

--On Step ten of CentOS 4.6 Server Setup: LAMP, Email, DNS, FTP, ISPConfig (a.k.a. The Perfect Server) i was unsure what to put on the follow postconfig step. Based on my question above... i didn't know what to put.

postconf -e 'mynetworks = 127.0.0.0/8'

--One last one.. If i have ISPConfig installed and working properly. Is there any issues with following the set up for DKIM With dkim-milter to implement Postfix DKIM?

I think that is all for now.

I want to give kudos to all that contributed on the how to's this is a great forum to teach folks...

 

Please don't double-post!