The March 2017 Release (build 17.0.17069.01) is live: http://mfcmapi.codeplex.com.
I apologize for this: https://github.com/stephenegriffin/mfcmapi/issues/29. Large icons were not intentional. As evidenced from looking at every other application I’ve looked at, high DPI is hard.
Please continue to report issues on Github. Codeplex is only being used to host our download. Issues reported there may or may not ever be seen (if I could turn off issue reporting on Codeplex I would)..