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. Exchange administrators may misinterpret the function of this option: They may expect Exchange to reject e-mail messages that originate from unresolved domains.
Some messaging systems verify the existence of the e-mail domain of the sender before they accept a "Mail from: user@domain.com" 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 5.5 and later do not use this feature.
In Exchange System Manager, 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.
If you enable the
Perform Reverse DNS Lookup for Incoming Messages option, you may have some performance degradation issues because of misconfigured DNS records and/or intermittent connections to the Internet. Therefore, you may want to disable this option when the Internet mail delivery is slower than expected.
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.
For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base:
258745 (http://support.microsoft.com/kb/258745/EN-US/) XIMS: Internet Mail Service Displays SMTP Banner Slowly
198981 (http://support.microsoft.com/kb/198981/EN-US/) XIMS: SMTP Messages Not Being Delivered to Certain Domains
262571 (http://support.microsoft.com/kb/262571/EN-US/) XCON: Internet Mail Service Registry Entry for DisableReverseResolve Does Not Map to Default SMTP Virtual Server After You Upgrade to Exchange 2000