Step 1 – Get your email out of the .pst files.
Install the readpst package.
sudo apt-get install pst-utils
Now create the directory where you will want the extract email files to be placed.
mkdir pst-export
Next execute the readpst command against a .pst file.
readpst -D -M -b -o pst -export archive.pst
UPDATE: Ian Major commented on a simpler solution. “Works great, after reviewing the options for readpst I changed the command line to be ‘readpst -M -b -e -o pst-export archive.pst’ which doesn’t import deleted messages, and outputs with the eml extension, which means the rename isn’t required.”