Hi guys,

I happen to be on two ISPs [therefore two public IPs. My mail server uses an ISP [ISP-A] whose link which has been annoyingly erratic since yesterday. I wish to route my outgoing emails through the other ISP [ISP-B], but some servers reject our mails when we use that link due to inconsistent PTR records. What I mean is this: mail.mydomain.co.ke resolves to my ISP-A [public] IP address. When I route to ISP-B, the EHLO message would show a connection coming from mail.mydomain.co.ke, but the PTR would not be equal to the IP given by ISP-B [from which the email actually originates] and that is why some mail servers drop the connection at that point.

Now my question: Is there a way I can combine dvert traffic to go out through my ISP-B box such that traffic appears to be from ISP-A? I tried using SNAT yesterday and it didnt work. 

Experiment: I was also wondering whether it is possible to route traffic based on the destination port, i.e. my mail and squid proxy server is 192.168.80.1/24 and also has 172.16.10.2/29. The ISP-A box is 172.16.10.1/29 and ISP-B is 172.16.10.3/29 [not their real IPs :-P]. I would like to make the default gateway for my mail and internet server 172.16.10.3, but route outgoing SMTP only traffic through 172.16.10.1. I know port numbers are dealt with in the transport layer while routing is a lyer 3 affair, but Ibelieve all things are possible in computing.

I would appreciate your ideas, suggestions, criticisms and even blank replies as are normally sent by some.