sudo apt-get install libemail-outlook-message-perl libemail-sender-perl
from a command line. Use
msgconvert *.msg
to convert every file in a directory at once. MSGConvert will produce copies of your .msg-files with the suffix .msg.eml
M. Banko, M. Cafarella, S. Soderland, M. Broadhead, and O. Etzioni. Proceedings of the 20th International Joint Conference on Artifical Intelligence, page 2670--2676. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2007)