Updated first post with links to sources.

Concerning the requirements, i suggest to run:
ldd /opt/claws/bin/claws-mail.bin

and for the plugins:

ldd /opt/claws/lib/claws-mail/plugins/*PLUGIN_NAME*.so

to check if you have all the required libs. (there are a lot of required libs to make them work!)

For Fancy webkit html viewer, don't forget to install libsoup-2.26 and libwebkit-1.0...