winpm-32.exe in Pegasus Mail (aka Pmail) v4.72 build 572 allows code execution via a crafted ssgp.dll file that must be installed locally. For example, if ssgp.dll is on the desktop and executes arbitrary code in the DllMain function, then clicking on a mailto: link on a remote web page triggers the attack.
https://packetstormsecurity.com/files/142606/Pegasus-4.72-Build-572-Remote-Code-Execution.html