XFOR: Internet Mail Service Very Slow with High Message Volume

• Microsoft Exchange Server, versions 5.0, 5.5

SYMPTOMS

You may experience either of the following symptoms:

• When an extremely large number of Simple Mail Transfer Protocol (SMTP) messages are sent through the Internet Mail Service and the Internet Mail Service is unable to resolve some of the Domain Name System (DNS) addresses associated with the messages, the Internet Mail Service may take a long time to send the messages.
  
  -OR-



• When the outbound Internet Mail Service message queue contains a large number of messages, the Internet Mail Service may take an unusually long time to start.

CAUSE

These problems can occur for the following reasons:

• The rate at which the Internet Mail Service delivers SMTP messages is limited in part by the number of resolver threads and SMTP worker threads that are available. If message volume is very high and DNS name resolution is frequently unsuccessful, the number of available threads can become very low.



• When you start the Internet Mail Service, it processes the destination domain list. The method by which it processes the destination domain list can be inefficient, particularly when the outbound message queue contains a large number of messages.

WORKAROUND

You can increase the number of resolver threads and SMTP worker threads that are available when the Internet Mail Service starts, but only by increasing the value assigned to the ThreadsPerProcessor variable.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.0.

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.

This fix has been posted to the following Internet location:

ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/Eng/Exchg5.0/Post-SP2-IMS/

S E R V P A C K

MORE INFORMATION

After you apply the fix, three new registry values are available under the following registry key:

   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIMC
   \Parameters 

   Value Name            Value Type   Description
   -----------------------------------------------------------------------
   SMTPWorkerThreads     REG_DWORD    If this registry value exists, it
                                      represents the number of SMTP worker
                                      threads that are available when the
                                      Internet Mail Service starts.

   ResolverThreads       REG_DWORD    If this registry value exists, it
                                      represents the number of resolver
                                      threads that are available when the
                                      Internet Mail Service starts.

   DestDomainThreshold   REG_DWORD    If this registry value exists, it
                                      represents the number of
                                      DestinationDomain objects that are
                                      cached before the Internet Mail
                                      Service attempts to reduce the size
                                      of the destination domain list. 

Additional query words: ims internet mail connector imc

Keywords : XFOR
Version : WINDOWS:5.0,5.5
Platform : WINDOWS
Issue type : kbbug