A Brief History of MFCMAPI
MFCMAPI Articles
Blog entries on MFCMAPI/MAPI Editor (archived)

MFCMAPI Addin Development
Sample add-in for creating contacts, appointments, tasks, etc.

When debugging MAPI or Outlook, add Microsoft's public symbol server to your debugger's symbol path:

https://msdl.microsoft.com/download/symbols

For MFCMAPI and MrMAPI, matching PDB archives are available alongside the executable archives in the GitHub releases. Download the PDB archive for the same release and architecture as the executable, then extract the PDB alongside the EXE.

Under Tools > Options > Debugging > Symbols, add the URL as a symbol-file location. While debugging, use Debug > Windows > Modules to load symbols and inspect Symbol Load Information.

Append the server to your symbol path, using a local cache directory, then reload symbols:

.sympath+ srv*C:\Symbols*https://msdl.microsoft.com/download/symbols
.reload

MSDN MAPI Documentation
Exchange Protocol Documentation
MAPI Mail List
ExchangeDev Blog (archived)
EHLO Blog
EWSEditor