I had a look at this since it doesn't really require much brainpower and I want to stay somewhat busy when up. A few small remarks about the config on Windows:if you're interested at all in building Epyrus, I think you'll be surprised by how familiar the build process is...
http://www.epyrus.org/build.html
1) --disable-eme is no longer a thing and will error the builds
2) The WIN32_REDIST_DIR is incorrect; current visual studio versions use {root VS dir}\VC\redist\MSVC\14.nn.xxxxx\$BUILD_ARCH\Microsoft.VC143.CRT where 14.nn.xxxxx depends on which update of VS you have installed (my current one is 14.38.33135)
Also, as an aside, for general optimization, you may want to think about using --disable-skia since a mail client won't actually use canvas drawing (and there's still the cairo fallback for that if needed) which can seriously cut down on build time for some, as well as reduce resulting binary size, complexity and potential bugs. Similarly, you may want to consider not building AV1 because I don't see that kind of codec playback being necessary for mail display?