PRB: Unable to Make More Than 256 Connections to Different Mailboxes Over a Short Period of Time (305619)

CAUSE

All WebDAV requests to an Exchange server called under a single-user context are pooled under one session that is limited to 256 concurrent connections. This limit is due to the way that the session count is stored in memory. WebDAV exposes this limitation because it keeps connections open for 10 to 15 minutes.

RESOLUTION

To resolve this problem, obtain the September 2003 Exchange 2000 Server Post-Service Pack 3 (SP3) Rollup. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

824282 September 2003 Exchange 2000 Server Post-Service Pack 3 Rollup

Alternatively, you can work around this problem in the following ways:

Pause after each group of 256 connections, allowing the other sessions to timeout and new sessions to be created.
If the code is running in a COM+ component as a specific user, adding additional server packages running under different user contexts will allow an additional 256 connections per package.
Use another provider to access the Exchange mailboxes (for instance, ADO).

MORE INFORMATION

Steps to Reproduce Behavior

Create 300 mail-enabled users with the alias naming convention of user(x), where x is the number 1 to 300.
Send an e-mail with the title "Test" to each of the 300 mailboxes.

Run the following code in an Active Server Pages (ASP) page:

<% Response.Buffer = TRUE
server.ScriptTimeout = 5000
Dim Rec 
Dim conn 
Dim strURL 

   For mailboxloop = 1 To 300
      strURL = "http://servername/exchange/user" & mailboxloop & "/inbox"
      Response.Write strURL & "<br>"
      Response.Flush
      strURL = strURL & "/Test.EML"
      response.write "Open: " & strURL & "<br>"
      Response.Flush
      patchmail()
   Next

Sub patchmail
 
    Dim intStartPos 
    Dim oRequest 
    Dim strTemp 
    Dim strXML 

    strXML = "<?xml version=""1.0""?>"
    strXML = strXML & "<D:propertyupdate xmlns:D='DAV:' xmlns:m='urn:schemas:httpmail:'>"
    strXML = strXML & "<D:set>"
    strXML = strXML & "<D:prop>"
    strXML = strXML & "<m:read>1</m:read>"
    strXML = strXML & "</D:prop>"
    strXML = strXML & "</D:set>"
    strXML = strXML & "</D:propertyupdate>"

    Set oRequest = Server.CreateObject("MSXML2.ServerXMLHTTP")
    With oRequest
        .Open "PROPPATCH", strURL, False
        .setRequestHeader "Content-type:", "text/xml"
        .Send (strXML)
    End With
    If (oRequest.Status <> 207) Then
        strTemp = "Error, status = " & oRequest.Status & " " & oRequest.statusText & "<BR>"
        Response.Write strTemp

    End If
    Set oRequest = Nothing
Exit Sub
End sub
%>

The first 256 users open without problem, but from 257 on, you receive HTTP 500 errors.