I've been "recruited" to help solve this issue for a friend with a small business.
Long story short, SBS2003 running exchange. Everything works pretty well (except certificate issues!) but their broadband is 1mb. After weeks of nagging ISP to upgrade the line to 24mb, they have finally done so on another line.
Every attempt to change over to the new modem/line has failed. Internet access is fine but all incoming mails are blocked and outgoing mails are very slow (1 - 2 hours).
I've opened all of the ports nessesary and even tried 3 differnent modems. (2x BT voyager 2110 & 1 linksys).
The original line is fixed IP setup with an old ericsson modem but it's only ADSL. NAT is disabled on it and it's plugged directly into a wireless router which is configured with the port forwarding.
The new line is PPoE with fixed IP and of course a different DNS. I've tried it with to correct port forwarding but no joy.
I've tried it with NAT disabled........and no joy
I've tried it with NAT disabled and plugged into the pre-configured wireless router (after changing the WAN settings to match)...... and no joy
Am i missing something or should i retire, crawl under a rock and never touch a computer again!!!!!