SMTP server or "forwarding"?

[Alexander Dalloz]

Am Sa, den 27.08.2005 schrieb Jonathan Berry um 7:11:

> Okay, a lot of ISPs now block port 25 out to anything other than their
> SMTP server.  In some situations, it would be nice to circumvent this
> to get to another SMTP server if one is not available.  So what I had
> though is to setup my FC4 linux box to listen for SMTP traffic on a
> non-standard port.  Actually, I could just have my hardware router

Client port and daemon port are not the same, as they are for different
transmission directions. So if the ISP blocks outgoing port 25, why
letting the MTA listen on a non-standard port for incoming connections?

> forward whatever port to 25 on the computer, so the non-standard port
> part should be easy.  It would be nice to have a workable solution
> with as little as possible.  Does anyone know of some way that I could
> maybe take any traffic to my server on my chosen high port and forward
> it along to my ISP's SMTP server on port 25?  It sounds possible, but

Other MTAs do not know of any non-standard ports you may use. There is
no "trick" to make them know what you may expect.

> sketchy enough to where it might not be.  Any ideas?  I figure I could
> always just setup my own SMTP server and that should work.  But I
> would need to make sure I did that right as I do not want to aid in
> the spread of spam and/or viruses.  Since it would be on a strange
> port, it shouldn't be as big a problem, if at all.  Any ideas on that
> point?  So, what do you think of my idea and options?  If I were to go
> the route of setting up my own SMTP server (perhaps even so far as a
> whole email server) any tips as to where to start looking for info on
> doing this right?

I do not really understand your aim. If your ISP blocks outgoing port
25, then he does for good reasons. He on the other side offers you to
send mail using his mail exchanger as a smart host. That is a standard
practise. If the ISP also blocks incoming port 25, you then have not any
choice and trying to run an MTA on that connection is wasted time. It
can't ever be fully functional, too you will hurt your ISP's rules.

> Jonathan

Alexander


-- 
Alexander Dalloz | Enger, Germany | GPG http://pgp.mit.edu 0xB366A773
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