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SecurExchange - > How To
How do I delete an email that has failed Reverse DNS Lookup?
Exchange Server and Reverse DNS Lookup Background:
Some messaging systems verify the existence of the e-mail domain of the sender before they accept a "Mail from: firstname.lastname@example.org" Simple Mail Transfer Protocol (SMTP) entry at the beginning of a new message delivery session. If the domain name cannot be resolved by means of Domain Name System (DNS), the session is disconnected and an error 501 is generated. This behavior is mainly used to prevent you from receiving spam (unsolicited e-mail messages). Microsoft Exchange Server 2003, 200, and 5.5 do not use this feature.
For Exchange Server, the Perform Reverse DNS Lookup for Incoming Messages option does not have the same function of the feature that had been previously described (the function to prevent the receipt of spam e-mail messages). When the preceding option is used, Exchange Server performs a DNS query to resolve the originating Internet Protocol (IP) address of the incoming messages to a host name. Then, the host name is attached to the headers of e-mail messages.
Enable Exchange Server to perform Reverse DNS Lookup:
In Exchange Server 2003/2000 the Perform Reverse DNS Lookup for Incoming Messages option is located on the Default Virtual SMTP Server Properties dialog box: On the Delivery tab, click Advanced .
By default, Exchange Server 5.5 performs a reverse lookup operation on all connections. This default operation, however, can be disabled by using a DisableReverseResolve registry setting.
Define a rule to handle messages failing Reverse DNS Lookup:
From the Spam Blocker tab in the Header Filtering section, click Header
In the Token field, select "received"
In the Header field, type "] RDNS failed)"
In the Action list, select Delete Message or any of the previously defined actions
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