Getting around ISP sendmail (port 25) block (Version 2)

skill · n00b Joined: 15 Apr 2004 Posts: 9

Getting around ISP sendmail (port 25) block (Version 2)

First of all, everyone who did read this about how to get around isp block on this[1] link found out that the solution to get mail was to add a rule to iptables telling it to redirect incomming connections at for example, port 9999 to port 25 internally on the server.

But as everyone knows, this is only the first problem, what I belive is more important is how to get traffic from another computer, which has an open port 25, to route the mails to my computer at port 9999. Whether this is done by using SSH-tunnel or some other great tunnel-software is offcourse intresting but im looking for the perfect solution, which would be the same as done above but with what i belive is the greatest firewall tool ever, iptables.

CAN YOU DO IT?

[1] https://forums.gentoo.org/viewtopic.php?t=57796

cudeso · n00b Joined: 10 Dec 2003 Posts: 36 Location: Brugge

splooge · l33t Joined: 30 Aug 2002 Posts: 636

Possible? Sure. Probable? No. Feasible? No. Will it work well? Not a chance.

You'd have to configure (err, get the administrators of the smtp server that's sending you mail -- one of a billion on the internet) the server that's sending you the e-mail to use port 9999. You think AOL is going to configure their servers to do that for you and break an internet standard?

Port redirection would work but no way you're gonna get all the servers on the internet to recognize your special case port at 9999.

If your inbound port 25 traffic is blocked, you're screwed. No mail server for you.
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kpack · Tux's lil' helper Joined: 29 Mar 2004 Posts: 137

Are you sure your ISP blocks inbound traffic on port 25? My last ISP blocked outbound traffic on port 25 to stop customers from spamming. They didn't block inbound port 25 connections, so it didn't stop me from operating my own mail server.

The only hitch was that my mail server had to forward outgoing mail to the ISP's mail server. I use PostFix, so I did that with the relayhost parameter:

fleed · l33t Joined: 28 Aug 2002 Posts: 756 Location: London

Even if they block your incoming 25 you could get a service that redirects your mail for you, I think www.zoneedit.com does it. For free too.

MadOtis · Posted: Fri Apr 16, 2004 11:19 am Post subject:

I use DynDNS.com to handle my redirects. What they do is create what they call a mailhop, or webhop. These are real-world addresses that actually point to their servers. They in turn redirect or forward the request to whatever url you specify when you set up the hop. So, I can create a URL like so: www.fredco.com, which would be publicly available to the whole internet, and where it would possibly end up on my machines would be sproing.fredco.com:8888. The same concept works with their mailhop service, but it's implemented a little differently because you're not dealing with a browser, and thus, does not handle redirects well.

HTH,
Randy