Route Traffic through Client

[MatthiasS]

Hi,

at the moment my ISP can't give me IPs where I can edit reverse DNS entries.

Now I have three small debian (6.x)  servers with IPs where I can set these entries as I like.
These servers are connected with my LAN via OpenVPN (auth via certs).
Incomming traffic I can route through the tunnel (rinetd on servers).

Now, is it possible to route outgoing traffic through these tunnels, too?
So, that for example all the traffic on target port 25 from my mailserver should go through the tunnel and use the external ip of one of the servers?

Thanks!
Matthias