Email SMTP Sending

[CH]

Hello all,

This is a weird problem I am having.

Software used:
Qmail, Qmail-Scanner, courierIMAP
O/S = Fedora 5
Virtual Domains

I can send email from my own network from my email client just fine. But
when I try setup the email client from outsite my network, I get this:
[ERROR]
The message could not be sent because one of the recipients was rejected
by the server. The rejected e-mail address was 'email at example.com'.
Subject 'Test', Account: 'BW(Lists)', Server: 'mail.example.com',
Protocol: SMTP, Server Response: '451 Dynamic IP Addresses See:
http://www.sorbs.net/lookup.shtml?xxx.xxx.xxx.xxx', Port: 25, Secure(SSL):
No, Server Error:
451, Error Number: 0x800CCC79
[/ERROR]

Also, when I use SquirrelMail it also works out of my network.

Now, I have static IP on my mail server, so this weird.

Hopefully I explained this right. If anyone has any questions please let
me know.

Thanks,
Will W.