Cut Mbox

The only thing this program does, is to copy the contents of an mbox
file to a number of smaller mbox files, each holding one message. These
output files will be in the same location and have the same file name
as the source mbox file, but with an undersore, a sequence number and
the extension .mbx added. It is strongly suggested not to run this
program on files in the Thunderbird profile, but only on copies in
other locations as Thunderbird will pick up these files.