32-bit DLL Call From MSMAIL32 to MAPILogon Fails

• Microsoft Windows NT Workstation version 3.5
• Microsoft Windows NT Server version 3.5
• Microsoft Mail for PC Networks, versions 3.0 and 3.2

SYMPTOMS

When making a dynamic link library call to MAPILogon from a 32-bit application directly to MAPI32.DLL, the call will fail from a custom command or a custom message in the Windows NT Mail client. The failure occurs in a MAPI error 2 (MAPI_E_FAILURE) which implies a general failure.

CAUSE

This problem occurs when the extension DLL is called while the Mail32 internal lock is on. When the DLL attempts to call out to MAPI, MAPI waits for the internal lock to be released and hangs.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 3.5. A fix to this problem is in development, but has not been regression-tested and may be destabilizing in production environments. Microsoft does not recommend implementing this fix at this time. Contact Microsoft Product Support Services for more information on the availability of this fix.