Email issues, relay failure

[Michael Powell]

Jon Radel wrote:

> On 2/25/12 10:26 AM, Bender, Chris wrote:
> 
>>
>> On telnet w IP it says unable to connect.
> ...
>> Its weird that the delivery on A says deferred connection timed out but
>> on tcpdump I see the port 25
> 
> 
> If you can't establish a TCP connection from A to your relay server on
> port 25, I'd expect all of the above.  If you can't establish a TCP
> connection to port 25 at all from A, I'd stop focusing on the details of
> the e-mail server on the relay machine (as they're likely to be beside
> the point) and start focusing on what is blocking the traffic from A.
> Have you audited all the firewalls involved?  To be really focused, if
> you see traffic (both ways) at the relay server when A tries to talk to
> port 25, but A is convinced that no TCP connection is established,
> either you're stomping on things at the relay server (do your attempts
> to telnet to port 25 fail immediately or just sit there for a good long
> time and then fail?), the reply packets from relay to A are getting
> mis-routed, or A is ignoring the packets coming in from the relay.  Can
> you ping from the relay to A?
> 
> There's a distinct difference between failure to establish a TCP
> connection (look to the network stuff) and the e-mail server giving you
> an error response rejecting your attempt to transfer mail or just
> quietly loosing the mail (look to the e-mail servers).
> 

It can also depend on a difference between residential vs business account at 
the ISP between them. If it was working fine and absolutely nothing was 
changed at either end, one posibility is an ISP implemented a policy of 
forcing mail submission to port 587, and whatever blocking they then started 
on port 25 is what broke the connection. 

-Mike