[PLUG] SMTP monitoring

[Derek Loree]

On Mon, 2004-10-25 at 16:53 -0700, Steve Bonds wrote:
> On Mon, 25 Oct 2004 15:39:54 -0700, Colin Kuskie wrote:
> 
> > When you get a bounce message and it says:
> > 
> > <user at remote_spot.org>... Deferred: Connection refused by server.remote_spot.org.
> > 
> > What does that mean?
> 
> A lot of things have to work correctly to get this message.  DNS
> properly looked up server.remote_spot.org.  The first packet in your
> attempt to set up a TCP connection to port 25 (SMTP) made it to the
> remote server through any firewalls or flaky connections along the
> way.  The remote server is up and sent you a packet back letting you
> know that there was nothing for you to connect with on that port.
> 
> Usually "connection refused" means that there is no software (mail
> server) up on the remote side, however it could also be due to a
> firewall someplace.  Some ISPs may block outgoing E-mail with
> "connection refused" in order to keep the spam-bot virus-infested
> masses in check.  However, this should show up for all mail
> destinations, not just one remote server.

An overloaded server would also return the same thing.  By overloaded, I
mean that the smtp server has reached its maximum number of concurrent
connections.  Most servers have a configurable limit on the number of
connections.  This is to help keep the kernel up and running under high
load.
> 
> If it's just the one remote server, it's probably their fault...

It's still their fault.

--
Derek Loree