[KLUG Members] sbc blocking port 25

[bill]

On Wed, 2005-03-02 at 09:04, Adam Tauno Williams wrote:
> > For some odd reason, tech support wanted me to list -all- the email
> > servers I may send to, which is a list too big to remember (no I send no
> > spam).  She assured me that any server I didn't list would get blocked. 
> > So they'll filter port 25 only allowing listed servers?  I'll check on
> > that and report later.
> 
> Any news?  Maintaining an allow list for clients seems like a great deal
> of work on their side.  They aren't blocking my Business DSL, yet.

I tried another domain name and it wasn't blocked.  So it looks like
they were lying.  Port 25 is either completely blocked or not.

> > The other thing you can do, if you have access to your sendmail servers
> > on linux (of course), is tweak iptables.
> > Let's say you want the server to use port 2525 (it will still accept
> > port 25), and your server ip is 12.34.56.78.  you can add this line: 
> > -A PREROUTING -p tcp -m tcp --dport 2525 -j DNAT --to-destination
> > 12.34.56.78:25
> 
> But that doesn't really help people trying to deliver too you.

I guess it depends on who "you" is.  Which machine(s) do you mean, the
one(s) behind my dsl or the ones out on the web?

www - mailserver - dsl - local machines

The prob was local machines could not do port 25 (outgoing) to the
mailserver on the web.  Everybody else could reach the mailserver fine
(unless they were being blocked on their dsl line, too.)

The problem I saw was outgoing port 25 (sending mail) on the DSL line. 
Being as I'm not running a mail server here, I wasn't testing incoming
port 25.

The iptables tweak above allows incoming SMTP for a server on the web to
accept port 2525 (as well as the normal 25).  That way I could access it
on the odd port.  If someone else also has outgoing port 25 blocked from
their machine, I can tell them to use port 2525.  

Now that my port 25 isn't blocked, I can go back and use it, and I may
leave the iptables tweak in case someone else runs into a similar
problem.

kind regards,

bill