Note that the API reference is maintained as part of libESMTP and may be built independently of this site, which may be what you actually want.
To build the website you will need Sphinx and the Sphinx readthedocs theme.
The API reference should be built first, so that documentation comments are
extracted from the source files. Create a symlink to source/reference
from
the docs
directory in the libESMTP distribution. Then use sphinx-build
to
create the site. For example:
$ ln -s /path/to/libESMTP/docs source/reference
$ sphinx-build source site-dir