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Q156711: XCLN: Exchange Win95 Client with DNS Polls for New Mail

Article: Q156711
Product(s): Microsoft Exchange
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): kbnetwork exc4
Last Modified: 22-DEC-1999

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The information in this article applies to:

- Microsoft Exchange Server, version 4.0 
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SYMPTOMS
========

When you configure a Microsoft Exchange Windows 95 client to use Domain Name
Service (DNS), it will typically poll for new messages every 60 seconds rather
than use push notification in which the Microsoft Exchange Server notifies the
Microsoft Exchange client that new message(s) have arrived.

CAUSE
=====

During Microsoft Exchange client initialization, it attempts to determine if any
network cards are available that use the IPX or TCP/IP network protocols. These
protocols can be used by the Microsoft Exchange Server to send push
notifications to Microsoft Exchange clients informing them of new mail
delivery.

When this protocol detection mechanism succeeds, the Microsoft Exchange Server
sends push notifications (via network datagrams) directly to the Microsoft
Exchange client. These datagrams instruct the client to poll for new mail (which
has just arrived). Typically, in the absence of new mail messages, an idle
Microsoft Exchange client communicates with the Microsoft Exchange Server once
an hour to ensure that communication with the server is still operational.

When this protocol detection mechanism fails to detect the presence of IPX or
TCP/IP, the Microsoft Exchange client will resort to polling for new mail every
60 seconds.

The protocol detection mechanism for TCP/IP uses a call to gethostname() that
returns the host name for the local computer.

Remarks in the Win32 Software Development Kit (SDK) about gethostname() state:

  This routine returns the name of the local host into the buffer specified by
  the name parameter. The host name is returned as a null- terminated string.
  The form of the host name is dependent on the Windows Sockets provider -- it
  may be a simple host name, or it may be a fully qualified domain name.

If gethostname() is called on a computer that has DNS disabled, the returned
value will simply be the computer name. If the computer has DNS enabled, the
host name itself can be specified (and it could be different than the computer
name) and a domain name suffix can be specified (something like org.com) which
is added to the host name when forming a fully qualified domain name for the
host.

An example of a simple host name is comp01. An example of a fully qualified
domain name is comp01.org.com

In the case of the Microsoft Exchange client, the buffer provided to this call is
sized at 15 characters, the maximum size of a NetBIOS computer name. When
Windows NT calls gethostname(), it always returns a simple host name that is
typically the same as the NetBIOS computer name and it will fit within the
buffer provided. On Windows 95, a call to gethostname() returns the fully
qualified domain name that typically exceeds the buffer length.

WORKAROUND
==========

Disable DNS on Windows 95, or remove the domain name suffix entry from the
Windows 95 TCP/IP properties DNS configuration property page, and ensure that
the host name specified is 15 characters or less in length.

STATUS
======

Microsoft has confirmed this to be a problem in Microsoft Exchange Server
version 4.0. This problem has been corrected in the latest U.S. Service Pack for
Microsoft Exchange Server version 4.0. For information on obtaining the Service
Pack, query on the following word in the Microsoft Knowledge Base (without the
spaces):

  S E R V P A C K


Additional query words: Hostname DNS Polling Pushing Push Poll RPC MSRPC Notification

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Keywords          : kbnetwork exc4 
Technology        : kbExchangeSearch kbExchange400 kbZNotKeyword2
Version           : winnt:4.0
Issue type        : kbbug

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