Move each of the 'm?' directories in current directory to another directory whose name is constituted by appending .mbox to each directory name and create a directory named Messages in this directory then move all *.emlx files into this directory
find . -name 'm?' -type d -exec mv '{}' '{}.mbox' ';' -exec mkdir '{}.mbox/Messages' ';' -exec sh -c 'mv {}.mbox/*.emlx {}.mbox/Messages' ';'