XADM: Exchange Win95 Client with DNS Polls for New Mail

ID: Q156711

The information in this article applies to:

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 


Keywords          : kbnetwork kbbug4.00 kbfix4.00.sp3 XADM XCLN 
Version           : winnt:4.0
Platform          : winnt 
Issue type        :

Last Reviewed: April 3, 1999