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Old 18th July 2009
guitarscn guitarscn is offline
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Default SMTP on non-standard port

I am running an OBSD mail server box, and running my own SMTP server along with it, but my ISP reserves port 25 for their own use (meaning they can't open port 25 for me even if they want to because they want it all for themselves ). I also cannot use my ISP's incoming and outgoing SMTP servers for some reason because they told me that I can only use those servers for internal e-mails, i.e. I can only send/receive from @myisp.com addresses (e-mails only from my ISP's domain).

So are there any alternative methods where I can use a port other than 25 to receive e-mails on my server? I can send e-mails fine, since any outgoing port will work and by default it will send to port 25 of any other e-mail server, but say if my friend@gmail.com tried to send me an e-mail, I would not be able to receive it because it will try to send the e-mail to my server at port 25 by default, but my port 25 is blocked. Or are there any other ports that all e-mail servers try to send to besides 25 (like 8080 besides 80 for http, which is how I configured my website because my ISP also blocks port 80 so I put Apache on port 8080 and everyone can see my website)?

Last edited by guitarscn; 18th July 2009 at 10:12 PM.
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Old 18th July 2009
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You can do this, but not as a standard, public access MTA, only a private-use MTA. e.g.: via dyndns.com's mailhop relay service.

It's probably easiest via pf(4). Here's an example excerpt from a redirected port 2525 to port 25 on the loopback interface:
Code:
rdr pass log on $external_nic proto tcp from any to any port 2525 \
        -> 127.0.0.1 port 25
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Old 18th July 2009
guitarscn guitarscn is offline
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So there's absolutely no way I can set this up as a public access MTA? I have a bunch of users on my mail server, but they can't receive e-mails from people sending e-mails via like Yahoo! or Hotmail or anything else like that. I must purchase a relaying service or buy SMTP servers to use?
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Old 18th July 2009
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Your ISP isn't reserving the port for their own uses, they're likely filtering/blocking it to help decrease spam.. i.e: protecting others from improperly configured servers.

You might be able to contact them and ask them to remove the block.. but if you're on a residential plan, you might be in violation their AUP, TOS.. admitting you're doing so would probably be a bad idea.

If however you're on a business plan, they may be more receptive to your request.. or they might be able to handle your mail requirements themselves.
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Old 18th July 2009
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Correct.

Port 25 is used for SMTP services. It is expected that the IP is a static address, and referenced by an associated MX record from an Internet-facing DNS server.

Your ISP is blocking port 25, most likely because you are in a dynamic IP address pool, and such pools are filled by millions of "zombie" platforms pumping spam to the world. Broadband users with Windows, mainly. ISPs will block not only outbound to port 25 (which would actually be helpful in curbing spam), they often block inbound port 25 (since dynamic users wouldn't normally use it).

You can either buy a static IP address from your ISP that includes an unblocked port 25, somehow convince your ISP to unblock port 25 (highly unlikely), buy an alternative relaying service, switch to another service provider, or give up on running a public access MTA.
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Old 18th July 2009
guitarscn guitarscn is offline
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Noooooooooooo

Okay, do you know what the cheapest place I can order is? Just for the SMTP servers so I can route mail from port 25 there to my CC box on a different port?
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Old 18th July 2009
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I don't know what's cheapest. You should try your own Google Fu, Grasshopper. Dyndns.com's mailhop relay, which is one I know about, begins at US$42/year.
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Old 19th July 2009
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Quote:
Originally Posted by guitarscn View Post
I am running an OBSD mail server box, and running my own SMTP server along with it, but my ISP reserves port 25 for their own use (meaning they can't open port 25 for me even if they want to because they want it all for themselves ). I also cannot use my ISP's incoming and outgoing SMTP servers for some reason because they told me that I can only use those servers for internal e-mails, i.e. I can only send/receive from @myisp.com addresses (e-mails only from my ISP's domain).
Sounds to me that you need different ISP.


Quote:
Originally Posted by guitarscn View Post
which is how I configured my website because my ISP also blocks port 80 so I put Apache on port 8080 and everyone can see my website)?
Sounds to me you really need different ISP.


By the way it is not very difficult to configure sendmail to use port which is
different than 25 it that is the mail server that you are using. I personally do not run my own mail server but I would be surprised it Postfix, Exim or Qmail do not have the option of using different port than 25.

I have one question for you. If your ISP is blocking all those different ports is he giving you reverse DNS? Of not even with
with static address your mail server is useless as any normal mail server will bounce mail from the server without reverses DNS.
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