Get it from the Github repository:
git clone https://github.com/pflanze/ml2json.git
For convenience, the (required parts of my) ftemplate and perllib libraries have been merged into this repository for now (in the future, I will properly package those libraries as separate CPAN modules and then just ask to install from there or from their own Github repositories).
The other non-standard dependencies can be installed on a Debian-derived Linux system using:
apt-get install libmime-tools-perl libemail-date-perl \
libhtml-tree-perl libmime-encwords-perl \
libmail-box-perl libtime-duration-parse-perl \
libdatetime-perl libemail-find-perl
Or install MIME::Tools, HTML::Tree, MIME::EncWords, Email::Date, Mail::Message::Field::Date, DateTime, Time::Duration::Parse and Email::Find from CPAN (run cpan or perl -MCPAN -e shell then install MIME::Tools etc.)
libemail-find-perl or Email::Find are only required if the scan_for_mail_addresses_in_body config option is set.
If you want to use json2csv, then also install JSON::SL from CPAN (not in Debian).
(Note that the version of libmail-box-perl from Debian Squeeze (oldstable, 2.095) does not contain Mail::Message::Field::Date. The version in Wheezy (2.105) does.)
There is no installation mechanism for the ml2json code itself (yet?). The programs can be run directly from the checkout (like ./ml2json or path/to/ml2json/ml2json). You could also add the path to the checkout directory to your PATH env variable, or you can symlink it to one of the directories in your PATH.
For usage information, run ml2json --help, and read usage and the other files in the "docs" folder.