Forward port 25 to another IP to send emails

dEM0nsTAr · 11-03-2009, 12:25 AM

I have just installed a Debian Lenny system with Postfix and Dovecot (used http://www.debianadmin.com/debian-ma...rrel-mail.html).
The machine is a member of the Active Directory (used http://awayand.wordpress.com/2009/02...y-w2k3-server/) and it can receive emails from the Microsoft Exchange Server 2007 in the network.
The problem is that it cannot answer or send new emails to users from the Active Directory because it tries to find the Exchange Server on the same IP as the domain controller.
Is it possible to route all outgoing traffic with port 25 to another IP?
Then it should be possible to reach the Exchange Server.

ptemmerman · 11-03-2009, 02:59 AM

Quote:

Originally Posted by dEM0nsTAr

I have just installed a Debian Lenny system with Postfix and Dovecot (used http://www.debianadmin.com/debian-ma...rrel-mail.html).
The machine is a member of the Active Directory (used http://awayand.wordpress.com/2009/02...y-w2k3-server/) and it can receive emails from the Microsoft Exchange Server 2007 in the network.
The problem is that it cannot answer or send new emails to users from the Active Directory because it tries to find the Exchange Server on the same IP as the domain controller.
Is it possible to route all outgoing traffic with port 25 to another IP?
Then it should be possible to reach the Exchange Server.

Sure. iptables and natting is what you need here.
More precisely DNAT (destination natting).

It would look more or less like:

iptables -t NAT -A OUTPUT -p tcp --sport 25 -d any -j DNAT --to-destination DEST_IP

dEM0nsTAr · 11-03-2009, 04:02 PM

Thanks for the fast reply but it doesn't work.
But it worked with

Quote:

iptables -t nat -A OUTPUT -p tcp --dport 25 -j DNAT --to-destination IPOFEX

where IPOFEX is the IP from the Exchange Server.