The reverse DNS lookup for your mail server IP address is misconfigured.
There is a reverse DNS (PTR) record established for your email domain name, but the name it points to does not contain any valid DNS "A" records that point back to your mail server's IP address.
This condition alone does not cause email to be rejected. However, if you received this error, then there were also other criteria that may cause your email domain to appear suspect. Ensuring that your ISP has proper reverse-DNS records for your email domain name will help make your email is not rejected or blocked by other ISPs.
Please call your ISP or DNS provider and ask them to establish a proper reverse DNS record for your IP address, reflecting your correct domain name.
If you were directed to this web page by an error message received from mailer-daemon, this means your ISP or corporate mail server is probably misconfigured. Please notify the administrator of the mail service you are using of this error.