XCLN: Exchange Win95 Client with DNS Polls for New Mail

• Microsoft Exchange Server, version 4.0

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.

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 was corrected in the latest Microsoft Exchange Service Pack. 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