Configure postfix to send and receive mail through ISP?

[xstax]

Hi,
My setup is 2 x Ubuntu 9.10 (x64) servers with ISPConfig 3 installed as per the very clear how-to posted by Falko:

serverA.mydomain1.tld
serverB.mydomain2.tld

I have never run a mail server successfully before and I need help with configuration. I have a static IP.

1. My ISP allows two methods of routing mail - the information is here:
http://www.internode.on.net/support/.../secure_email/. They also are willing to help if I decide to run my own system but I'd rather use their service.

Can someone please help me with how to configure serverB.mydomain2.tld to use this service. For example - how do I configure postfix ..

2. I want to direct all mails from serverA.mydomain1.tld to serverB.mydomain2.tld internally (behind my router) and I wish to send out (to the WAN) and receive mails (from the WAN) on serverB.mydomain2.tld only. Will this be possible?

3. When setting up a DNS zone in ISPConfig 3 I notice that the control panel very handily sets up a number of "records" by default. Are there any more records I need to set up for mail boxes?

I hope my questions are clear. All help much appreciated.