Email Failing to SOME Domains after ISP change

Here's the situation:

A client of mine has a Microsoft SBS 2003 server with Exchange 2003 currently running on it (will be upgrading that in the next few weeks but that's another story). Emails were sending and receiving perfectly fine until two weeks ago. At that time, my client went through an ISP change - sort of. They switched from AT&T DSL to AT&T fiber. At that time, their IP address also change. Now emails are not going through to SOME domains.

In troubleshooting, I did download the SMTPDiag tool and ran it. Here are the results:

C:\Documents and Settings\admin\Desktop\SmtpDiag>smtpdiag ggasper@usenergyscienc
es.com attersonb@bellsouth.net

Searching for Exchange external DNS settings.
Computer name is FS01.
VSI 1 has the following external DNS servers:
There are no external DNS servers configured.

Checking SOA for bellsouth.net.
Checking external DNS servers.
Checking internal DNS servers.
SOA serial number match: Passed.

Checking local domain records.
Checking MX records using TCP: usenergysciences.com.
Warning: The TCP DNS query returned no results.
Checking MX records using UDP: usenergysciences.com.
Warning: No MX or A records were found for the local domain. If the records are
not configured, incoming mail can fail to be delivered to this server.

Checking remote domain records.
Checking MX records using TCP: bellsouth.net.
Checking MX records using UDP: bellsouth.net.
Both TCP and UDP queries succeeded. Remote DNS test passed.

Checking MX servers listed for attersonb@bellsouth.net.
Connecting to gateway-f2.isp.att.net [207.115.11.16] on port 25.
Error: Expected "250". Server rejected the sender address.
Failed to submit mail to gateway-f2.isp.att.net.
Connecting to gateway-f1.isp.att.net [204.127.217.16] on port 25.
Error: Expected "250". Server rejected the sender address.
Failed to submit mail to gateway-f1.isp.att.net.
Thomas BowersAsked:
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Alan HardistyCo-OwnerCommented:
If you have changed ISP's - you will need your new ISP to setup Reverse DNS on your new Fixed IP Address.]

Once that is done, the few domains you are mailing that reject you should be much happier.

Call your new ISP and ask them to set it up.

Alan
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KimputerCommented:
Nice diag tool (NOT! It only says it's failed, not the EXACT reason why.)
You should monitor the email traffic, or use telnet to see the actual error message.
Then check back here to see what the solution is:
http://rbl.att.net/block_inquiry.html

This is my error message, which I know why without looking up error codes:

550-xxx.xxx.xxx.xxx blocked by ldap:ou=rblmx,dc=att,dc=net
550 Error - Blocked for abuse. See http://att.net/blocks

I'm on a dynamic IP range, most mail servers will block these.
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Thomas BowersAuthor Commented:
Thank you for the quick response. Yes, if this resolves the issue, there will be much rejoicing from my client, the recipient and ever more so myself!

I suspected Reverse DNS but was unsure where to go to make the changes. I have sent AT&T support a request to make the changes. I will mark this question as solved as soon as the change is made and resolution is confirmed.

Again, thank you for the quick response.
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Alan HardistyCo-OwnerCommented:
You're welcome - it should resolve the issue (he says optimistically), but happy to answer more questions if it doesn't.

Alan
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Thomas BowersAuthor Commented:
Looks like we're all set. The only thing I will add is to make sure the PTR record matches what is set in your FQDN for your Default SMTP relay. I had to adjust to "mail.usenergysciences.com" since that is what I sent to AT&T's DNS support.
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