Note these are built automatically from Claws Mail CVS' sources and Debian packaging Subversion's sources.
For i386 architecture you have to add the following lines to your /etc/apt/sources.list (second line only if you want source packages):
deb http://www.claws-mail.org/debian/cvs/i386/ ./
deb-src http://www.claws-mail.org/debian/cvs/i386/ ./
For amd64 architecture:
deb http://www.claws-mail.org/debian/cvs/amd64/ ./
deb-src http://www.claws-mail.org/debian/cvs/amd64/ ./
Aditionally you may want to add the key used to sign the packages to your APT keyring to avoid the non-authenticated packages error message. If you have wget you can:
wget -O - http://www.claws-mail.org/debian/cvs/public.key.txt | apt-key add -
These repositories are updated nightly (from 00:00 UTC to 06:00 UTC), so you may experience breakages when updating between these hours.

