Microsoft KB Archive/292278

= Internet Information Services Simple Mail Transfer Protocol Service May Be Unable to Send Mail =

Article ID: 292278

Article Last Modified on 1/15/2006

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APPLIES TO


 * Microsoft Internet Security and Acceleration Server 2000 Standard Edition

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This article was previously published under Q292278



SYMPTOMS
The Internet Information Services (IIS) Simple Mail Transfer Protocol (SMTP) service installed on an Internet Security and Acceleration (ISA) Server 2000-based server may not be able to send mail, and the following error may be logged in the event log:

Event ID 4000

Source: SMTPSVC

Type: Warning

Description: Message delivery to the remote domain  failed. An internal DNS error caused a failure to find the remote server. 0000: c00402e7



RESOLUTION
To resolve this behavior, add a second Domain Name System (DNS) packet filter for the outbound Transmission Control Protocol (TCP) port 53:

Name: DNS TCP

Allow Packet Transmission

Custom: Protocol: TCP

Direction: Outbound

Local port: All ports

Remote port: Fixed port

Remote port number: 53

Default Internet Protocol (IP) addresses for each external interface on the ISA Server computer

All remote computers



MORE INFORMATION
ISA Server is configured with packet filters for inbound and outbound SMTP traffic. The default DNS client packet filter is also in place. From ISA Server, you can use telnet for the outbound SMTP traffic on port 25 and you can resolve names by means of DNS. The SMTP service receives mail, but outgoing mail remains in the queue.

When you trace how the SMTPSVC service delivers mail, this service uses a TCP DNS query for the mail exchanger (MX) record of the domain to which it is attempting to deliver mail. The default DNS filter in ISA Server is only enabled for User Datagram Protocol (UDP) queries. The addition of a second filter for DNS on TCP port 53 enables the DNS queries to work.

Keywords: kbprb KB292278

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