MAPI problems within ActiveX control

Hi,

We have developed an ActiveX-based web application using VB6.0 that uses MAPI to send emails via our corporate Exchange server. The application runs inside our firewall on our company's intranet.

The emailing ascpect of the application worked flawlessly during all phases of testing, however, once in production, certain users began reporting problems sending emails.

During our testing cycles, we would download the ActiveX control (CAB file) from a development IIS server and the emailing would work without a hitch. Now that the application is being used in production, the CAB file is being downloaded from a production IIS server. The physical location where the ActiveX CAB file is stored is the ONLY difference that exists between the development and the production environments. The CAB files are identical in every respect.

We're wondering if this difference may be a reason why for some users, the emails aren't going through. If it is, we are quite puzzled as to why it would matter where the application is being downloaded from.

I should also explain that the code that does the emailing uses MAPI. This code, part of the ActiveX control, executes locally on the client's machine. As you know, all code inside ActiveX controls executes locally on the client and not on the server. In fact, the IIS servers only serve as a storage container for holding the ActiveX CAB files so that they can be accessed for download. MAPI, when executing on the client, depends on a few DLLs that need to be present on each client. We have verified that all users of this application have these DLLs and are all of the same version.

What is even more odd is that when we request a user, who is having problems emailing via this application, to run a copy of the application that is hosted on the development server, the emails work fine.

Has anyone had a similar experience? If so, I'd love to hear from you. Any advice would be appreciated.

Regards.

H.