xdkim was forked of libdkim-1.0.21. The libdkim project is/was marked as inactive on sourceforge in 2016. At time libdkim-1.0.21 was the last version available.
Initial the code was stripped down, all WIN32 stuff was (hopefully) re- moved. The shared library functionality is gone. The library is linked statically with the executable xdkim, which is the renamed successor of the former libdkimtest.
xdkim was tested to run on Linux-like systems only.