The file readme.txt explains how to build and deploy LotusExtension.dll. If your build environment is not preset, you will need to execute vcvars32.bat (or an equivalent pre-build setup file) before executing nmake.
PROGRAM - LotusExtension.dll - Lotus Notes Mail Extension Manager To build: enter "nmake LotusExtension.mak" from a command prompt. FILES *LotusExtension.c - Main C source code file for Lotus Extension Manager *LotusExtension.h - Constants and function prototypes. *LotusExtension.mak - Make file for Windows 32-bit. *LotusExtension.def - Module definition file for Windows 32-bit. *readme.txt - This file. To install and run this program: 1. Exit Notes if it is running. 2. Copy LotusExtension.dll to the Notes program directory. (usually C:\Program Files\Lotus\Notes) 3. Edit the notes.ini file. If an EXTMGR_ADDINS entry does not exist, add EXTMGR_ADDINS=LotusExtension.dll If an EXTMGR_ADDINS entry already exists, add ",LotusExtension.dll" to the end of the existing line. Save the modified notes.ini file. 4. Launch Notes. 5. Lotus email will now be filtered through LotusExtension.dll