O.K. I'm new to virtual domains and virtual emails so I thought I would
use a "kit" and so I chose ISPConfig(as it makes domain setup/ changes easy). I followed the "perfect debian etch setup" as per ISPConfigs site sudgestions and changed my host and domain names to match my system.
Everything works as it should, but the email. I can login to the users via there clients and send mail from them but I cant receive emails through them. I get an error:

<user@mydomain.com>: host
mydomain.com[www.xxx.yyy.zzz] said: 554 5.7.1
<user@mydomain.com>: Relay access denied (in reply to RCPT TO
command)

This should not be a relay for my local users, but I have some remote users on public ip's(dynamic) that need the relay.
My config files look like the "kit" files save for the host and domain names are mine not the "kits"
I would like to know what causes this in a virtual setup and how I can fix it.
Thanks

Have you specified the network address range(s) in mynetworks option in /etc/postfix/main.cf?

Yes, I have tried to use both the default (127.0.0.1), and the local ranges. As I am behind a firewall that provides a DMZ I would rather not use public ip ranges (I cant have an open relay). This may be a DMZ problem, I'm not 100% sure but all other server functions work remotely.
It's just sending email to the server.

The error you are reporting is consistent with either or both;

No MX directive as far as external access is concerned and/or no specification of network ip address ranges and/or closed ports.

You would need an MX record to receive mail from the Internet and you would have to specify the address range (in main.cf)that it came from. No MX record and there will be no way for your server to be found on the Internet. If you don't specify an IP range of addresses in Postfix it won't accept connections from them. Specifying a network IP range in the main.cf file means that you will accept connections from that range only and does not make it an open relay. eg. specifying a network range of 192.168.0.0/24 means that it will receive and send mail for any system in that range only. The address 127.0.0.1 is localhost only i.e. the box the server is installed on.

If you make amendments to Postfix main.cf then you need to restart the server again;

from a root consol do: /etc/init.d/postfix restart

To receive mail you need to open port 25. To send mail you need to open port 110.

I hold my own DNS for this server and have two public dns's that also hold my zone info including the mx record incase my dns fails(has happend before), but I will retrace my configs and let you know.
Thanks