I started getting NDRs on mail sent to sbcglobal.net a couple weeks ago. The end of the message stated to see att.net/blocks for more information. I filled out the form and was notified that we were not on blacklist. I then started research on other possible causes.
I first went to mxtoolbox.com and ran test (SMTP diag, reverse lookup, blacklist) and passed all.
I then went to dnsstuff.com and ran their Mail Server Test Center. This test showed I was missing SPF records. I created the TXT records for my domain at networksolutions.com and ran the Mail server test the next morning and passed all. Test email to sbcglobal.net resulted in immediate NDR.
Next I ran the Domain Doctor test on dnsstuff.com. This test stated I Failed the SMTP greeting(Checks the SMTP for validity). I created the needed A records on network solutions to reflect my Barracuda spam box(barracuda.company.com 7200 6x.x2.9x.3x). Ran the Domain Doctor test the following day and passed. Test email to sbcglobal.net resulted in immediate NDR.
I had a friend take a look at the NDR today and he noticed something immediately. The FQDN in the NDR was server.internaldomain.loca
l. I went to Advanced Delivery in the Default SMTP Virtual Server Properties and changed the Masquerade domain to publicdomain.com and the FQDN to email.publicdomain.com. Test email to sbcglobal.net resulted in immediate NDR but now with updated FQDN. The current NDR is as follows:
The following recipient(s) cannot be reached:
firstname.lastname@example.org on 1/5/2012 11:41 AM
The message cannot be delivered due to a configuration error on the server. Please contact your Administrator.
<email.companyname.com #5.3.0 smtp;553 5.3.0 flpd110 DNSBL:RBL 521< 6x.x2.9x.3x >_is_blocked.__For_information_see_http://att.net/blocks>
My friend stated that he thought my IP was on the blacklist so today I filled out the form and while typing this post I received and email stating again that I was not on the blacklist.
Sorry for the long post but I wanted to let you know I have researched and tried several things but I am out of ideas.
Any help on this would be greatly appreciated !