Hi, Keith-
In my experience, most oddball problems with mail are DNS-related in some
way.
But I've specifically tried sending tests from domains that are NOT using
the gateway and these still get the '450 busy' response.
How are you sending the telnet from the domains? Does each domain have its
own mail server?
One idea: See if you can get the gateway provider to try the telnet test
directly on the gateway server. You may want to try using your inbound
gateway also as an outbound gateway if you find that telnetting from the
gateway works.
Second idea: Do you have SPF records for the domains? Are they correct?
One way this MIGHT work:
- You start the telnet session
- ATT checks reverse lookup on your mail server's IP
- ATT tries a forward lookup on the returned FQDN to see whether it matches
the IP
- ATT checks for an MX record covering the domain and looks to see whether
that returns the IP
- ATT checks for an SPF record to see whether the IP is authorized.
ATT MIGHT reject the connection if one or more of the following are true:
- There is no reverse lookup for the IP
- There is a reverse lookup but the FQDN doesn't resolve to the IP
- There is no MX record for the domain
- There is an MX record, but it doesn't resolve to the IP
- There is no SPF record
- There is an SPF record, but the IP isn't authorized
Just a few thoughts. There are certainly other explanations.
-d
----- Original Message -----
From: "imail" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, March 01, 2006 11:12 AM
Subject: Re: [IMail Forum] 450 busy, when delivering to att.net
Dave and Matti, thanks for your ideas; they got me thinking/testing in
some new directions, but I'm still pretty stumped.
Regarding the possibility of greylisting: "does the email deliver with the
next queue run?" No. Our mail server makes 5 attempts over the course of
several hours and usually all 5 attempts return the '450 busy' smtp
response.
Regarding our MX records: we are using a third party spam filtering
gateway for inbound mail on some domains, but not all domains. I hadn't
thought of this being a potential problem before. But I've specifically
tried sending tests from domains that are NOT using the gateway and these
still get the '450 busy' response.
To add to the mystery, I've discovered that the connections aren't failing
100% of the time. The connections are failing roughly 95% of the time.
About one out of every twenty attempts are delivered fine. When I try to
telnet to att.net's smtp servers from our mail server
(mail.addisontech.com), I get the exact same result: 95% of the attempts
return '450 busy', while 5% connect fine.
Telnet from my workstation (on a different IP address, but in the same
Class C IP range) results in 95% failure (450 busy). Telnet from my home
computer (through a completely different ISP) results in 100% success.
Coupled with the tests Dave ran, I'm not sure what to make of these
results. AT&T continues to assure us that our mail server IP is not being
blacklisted.
-Keith
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