It's late so I'm going to keep this brief but since we don't have any public content I wanted to get the word out. Exchange's CDO 1.21 was never tested and will not work with Kerberos authentication. While Outlook's version of CDO 1.21 does have Kerberos support, it is not suitable for use in serviced applications.
A lot people install Exchange System Manager on an IIS box in hopes of using CDO 1.21 inside an ASP application. Typically this ASP application was hosted on the Exchange server itself in the Windows 2000 days but Windows 2003 fully supports Kerberos and this seems like an opportunity to seperate the tiers a bit. What we see people wanting to do is seperate the ASP application to a seperate IIS server with integrated authentication turned on thus allowing users to use this internal web application to pull information from their mailbox or a public folder using their credentials against Exchange through CDO 1.21. What they find is that they get a MAPI_E_LOGON_FAILED error even though they verify the IIS application is running as the logged in user. The problem is that CDO 1.21 doesn't support Kerberos.
Unfortunately we can only offer workarounds. CDO 1.21 is old and being de-emphasized in Exchange 12. Here are your options:
...I thought I was going to keep this brief but I guess not. Anyway, like I said we don't have offical content up yet but I will update this post with the KB article when it goes public. Until then look into WebDAV.
...Update, here is the only offical explaination of this issue that is out there right now...
...the most important thing to take away is quoted below..
"EMSMDB32 on the client was modified to support RPC canceling instead of waiting on the server as well as RPC over HTTP and Kerberos authentication. EMSMDB32 on the server went through a series of multithreading changes to improve performance for server applications. EMSABP32 on the client gained the ability to rebind to global catalog servers, where the server version originally did not. MAPI32 was further adapted to work well with third-party providers, while the server version received additional fixes to the temp profile provider."
...Updated 6-02-06...Here is the KB link...http://support.microsoft.com/?kbid=918710
WebDAV can be a little cumbersome to work with. To be honest I'm never thrilled to use it, but that is only because of the way you interface with Exchange using WebDAV. WebDAV is a protocol, not an API. It is an extension of HTTP and provides more request