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Alternate port for SMTP

I've been using an alternate port for SMTP in conjunction with an upstream anti-spam/anti-virus service. The advantage has been multiple: crap traffic that relies on the MX record never finds its way to my WAN link, and crap traffic that randomly selects my WAN IP never gets past the firewall because I block all inbound traffic on port 25.

I will continue to use my external filtering service, but I'd really like to get some assistance in configuring the ASG to proxy for me on inbound messages; I can't see where the mail proxy could be configured for a different port for use in a situation like mine.

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0 BarryG over 15 years ago

The potential problem is that any other traffic on that port would get misdirected.
I'm not sure if reply traffic gets seen by DNAT, but if so, it's quite likely that it will happen.

Long ago, on another Linux firewall, I used to have a DNAT for ICQ, around port 4000, and I frequently would have problems surfing the web... I eventually realized that my PC was using incrementing ports for browser and other return traffic, and 4000 would occasionally come up.

Barry
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0 BarryG over 15 years ago

The potential problem is that any other traffic on that port would get misdirected.
I'm not sure if reply traffic gets seen by DNAT, but if so, it's quite likely that it will happen.

Long ago, on another Linux firewall, I used to have a DNAT for ICQ, around port 4000, and I frequently would have problems surfing the web... I eventually realized that my PC was using incrementing ports for browser and other return traffic, and 4000 would occasionally come up.

Barry
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