SYMPTOMS

PTR records are enabled but other mail servers cannot send mail to the server.

CAUSE

If PTR verification is enabled, the server may be unable to receive mail from some domains because these domains do not have PTR records defined.

SOLUTION

The following RFC provides useful guidance on which DNS entries should be created for domains.

- http://www.faqs.org/rfcs/rfc2505.html

It is best practice to have PTR records defined for A records. An MX record contains an A record and therefore by deduction must have a PTR record associated with its A record.

The tools available at www.dnsreport.com and www.dnsstuff.com are useful in diagnosing such issues.

MORE INFORMATION

What is a DNS PTR record?: http://www.mailenable.com/kb/content/article.asp?ID=ME020206

How to set up PTR records under Microsoft's DNS Server: http://www.mailenable.com/kb/content/article.asp?ID=ME020115

When sending messages to Hotmail, they appear in the Junk Mail folder: http://www.mailenable.com/kb/content/article.asp?ID=ME020241

Unable to send email to some domains, such as Hotmail, Yahoo, etc.: http://www.mailenable.com/kb/content/article.asp?ID=ME020003