sending mail from dmz with nated public ip does not work

[avbox55]

I have a dmz and there two nameserver and a mail server. Receiving mails on postfix works, but not sending. Everythime I try to send a mail with telnet, I get on the destination mail server an error, that the mail is rejected due to cannot find your reverse hostname [x.x.x.x]. The x.x.x.x address is the adress of the bridge from the isp, but there should be the public address from my mail server.

I added virtual ip interfaces for the public ip addresses and then a have firewall rules and nat port forwarding (forwarding dmz ip address to publich ip address).

How can I achieve that outgoing mail has its own public address and not the public address from the isp brdige?

[Fright]

add new outgoing nat rule for this ip