You need a Subversion client to access the Hedwig source repository. Once you have the Subversion client installed you can checkout the main Hedwig source tree with the following command or its equivalent in the client you are using:
svn co svn://svn.code.sf.net/p/hwmail/code/trunk hwmail
The above checkout will create a subdirectory named hwmail that contains the latest Hedwig sources.
This procedure explains how to install from the source distribution.
mvn clean package
If the above build fails on some tests, type the following:
mvn clean package -Dmaven.test.skip=true
mvn eclipse:eclipse