Here is an example of typical bounce message Since the vast majority, but by no means all, of email that originates from such addresses is spam, many spam filters refuse email originated from such sources. Many mail servers check PTR record against set of regular expressions to see if it matches a generic PTR such as "" or "". Thus, reverse DNS for IP address 1.2.3.4 is forward confirmed. Host name resolves to IP addresses 1.2.3.4 and 5.6.7.8. If there is a forward DNS lookup that confirms one of the names given by the reverse DNS lookup, then the FCrDNS check passes. Then for each domain name mentioned in the PTR records, a regular DNS lookup is done to see if any of the A records match the original IP address. For FCrDNS verification, first a reverse DNS lookup is done to get a list of PTR. FCrDNS, or Forward Confirmed Reverse DNS, is when an IP address has forward and reverse DNS entries that match each other.
0 Comments
Leave a Reply. |