MS Exchange CDO v1.21 Verification.

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When installed for Exchange 5.5 , these applications will use CDO.DLL to access mailbox items on the Exchange server. If you are having problems that may be CDO-related, it is a good idea to verify that you have the latest version of CDO.DLL for your Exchange version.

Note that if you are using Exchange 5.5 and your OWA installation is on a different server to Exchange, then you need to do this on your OWA/IIS server, which might not be your Exchange mail server. If they are different servers, the file version on the main Exchange server is not relevant to OWA problems. You should also be aware that all your Exchange Service Packs and patches need applying to the OWA server as well as the Exchange server. Many people are not aware of this.

An important potential problem to be aware of is that if you have installed MS Outlook on the server, it may have replaced the server CDO registration with its own. Outlook CDO is not suitable for server applications, and will cause strange, unpredictable errors, so you need to make sure that the server CDO registration has survived.

The first thing to check is to look in the registry and find out which DLL will be used to instantiate the "MAPI.Session" object. First, get the class CLSID from HKEY_CLASSES_ROOT\MAPI.Session\CLSID

This should be 3FA7DEB3-6438-101B-ACC1-00AA00423326 . Next, check the path to the server application for this CLSID at HKEY_CLASSES_ROOT\CLSID\{3FA7DEB3-6438-101B-ACC1-00AA00423326}\InprocServer32

This should point to either C:\WINNT\system32 (for Exchange 5.5), or C:\Program Files\Exchsrvr\BIN (for Exchange 2000 or 2003). If it points to somewhere like C:\Program Files\Common Files\System\Mapi\1033\CDO.DLL , then the registration has been replaced with the Oulook version, and you will need to re-register the server version with regsvr32.exe .

Once you have established that the correct version is registered, you will need to check the CDO.DLL file version to make sure that you have the latest file version (shown in bold in the table below) for your Exchange version. Here are all the CDO v1.21 file version numbers that I have seen, if you know of any others please let me know:
NB. I am not including any Outlook CDO.DLL versions here.

Exchange 5.5 CDO 1.21 CDO.DLL Versions
Location: C:\WINNT\system32

Exchange 2000 CDO 1.21 CDO.DLL Versions
Location: C:\Program Files\Exchsrvr\BIN

Exchange 2003 CDO 1.21 CDO.DLL Versions
Location: C:\Program Files\Exchsrvr\bin