IMS: Smtpsvc Queue Processing Is Slow When DNS Lookup Fails

• Microsoft Commercial Internet System, version 1.0

SYMPTOMS

The Internet Mail Server (IMS) may process mail slowly resulting in a backup of mail in the mail queue as well as in the pickup directories. The queue directory will contain a large number of .rtr files which indicates that multiple Domain Name Service (DNS) retries have occurred.

CAUSE

Excessive DNS query failures cause mail processing to perform slowly because IMS continually attempts to resolve the names against the DNS. The DNS lookup attempts use a critical section to ensure mutual exclusion when running the DNS lookup code. This causes all other queue processing that requires DNS resolution to stop until the current DNS lookup is complete.

RESOLUTION

Smtpsvc.dll was modified to resolve contributing issues with the handling of DNS MX lookups, and the handling of DNS lookup retries.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Commercial Internet System version 1.0. A supported fix is now available, but has not been fully regression- tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.