The "Perform Reverse DNS Lookup for Incoming Messages" Option Is for Host Name Resolution (297412)


The information in this article applies to:

  • Microsoft Exchange Server 2003 Enterprise Edition
  • Microsoft Exchange Server 2003 Standard Edition
  • Microsoft Exchange 2000 Server
  • Microsoft Windows Small Business Server 2003, Premium Edition
  • Microsoft Windows Small Business Server 2003, Standard Edition
This article was previously published under Q297412

SUMMARY

This article describes the Perform Reverse DNS Lookup for Incoming Messages option and how its function can be misinterpreted by Exchange administrators.

MORE INFORMATION

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 XIMS: Internet Mail Service Displays SMTP Banner Slowly

198981 XIMS: SMTP Messages Not Being Delivered to Certain Domains

262571 XCON: Internet Mail Service Registry Entry for DisableReverseResolve Does Not Map to Default SMTP Virtual Server After You Upgrade to Exchange 2000

Modification Type:MinorLast Reviewed:4/25/2005
Keywords:kbinfo KB297412
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