Magic Mail Monitor is an MFC-based application for Windows, originally written in the 1990s by Valeriy Ovechkin, that provides the ability to manage multiple POP3 accounts.
The SourceForge page for the project (as of the last released version) is: http://mmm3.sourceforge.net/
There is now a fork of Magic Mail Monitor with Tcl scripting support (i.e. for matching against header fields and performing some action) here: https://eagle.to/cgi-bin/mmm/ The fork also fixes several long-standing bugs in the code, reorganizes the source code files into a nicer directory structure, and supports Visual Studio 2010/2012/2013.
Multiple attempts have been made to contact the previous maintainers and the original author to notify them of the fork; however, no responses have been received.