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-   -   Changing pop3 port ?? (https://www.linuxquestions.org/questions/linux-networking-3/changing-pop3-port-269707/)

frzburn 12-23-2004 05:03 PM

Changing pop3 port ??
 
Hi, I would like to change the port of my pop3 service.
Here's the situation:
I tried to set up a mail server. I can send e-mails, it works perfectly by using my ISP smtp. But I can't receive e-mails. I suspect my ISP from blocking my port 110, just as he does with the port 80.

With the port 80, it was easy: I set my (apache 1.3) httpd.conf file to listen to port 8080, and tell my router to forward port 80 to port 8080. Works like a charm.
So I think I could do the same thing with pop3 (port 110), if I knew where (wich file) to change its port... I tried /etc/services, without success.


Of course, I registered a Dynamic DNS (dyndns.org) to make it easier to find me on the net.
I use Slackware 10 with 2.4.27 kernel
I'm using sendmail-8.12.11

Thanks!

cherylchase 12-23-2004 06:07 PM

Depends a bit on what mailer you are using. There's a discussion here that should be helpful:

forums.devshed.com/t209668/s.html

frzburn 12-23-2004 06:18 PM

Thanks for the reference. It clears things a bit.
I understand what the guy (dba_frog) says, but... if I can do it with http from port 80 to 8080, why not with pop?
So I'll keep seeking the sendmail docs, or at worse try qmail...

cherylchase 12-24-2004 09:33 AM

The reason why you can do it with incoming http but not incoming email is that you get to tell people who want to visit your web server that they should use a different port. But transport of email is distributed all across the net. When someone sends you an email, it may pass through a number of mail servers on route, and there's no way to tell them to talk to you on a nonstandard port.

I just realized that I'm confused about what you are actually trying to do. You said "can't receive emails", but then also mentioned pop3 and port 110. Pop3 is only used to transport email at the final stage, into the user's email client. Before that (between sender and receiver's mail host) it is transferred by smtp. You can't tell mail most hosts to talk to you with smtp on a nonstandard port (except for mail reflectors, mentioned in the devshed forum post linked above).

So if you want to run your own mail host, you need to be able to receive mail from any sender via smtp. They are only going to talk to you on port 25. Thus the need for a mail reflector.

There's a sort of helpful picture of this at http://computer.howstuffworks.com/email4.htm. As you see, port 25 is what connects your mail host to other mail hosts (and allows incoming mail). Changing the port used by pop3 will only affect communications between your mail client and local mail host (sounds like your client probably runs on your mail host in any case).



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