This submission type requires Moodle >= 2.3.
$ cd [moodle installation]/mod/assign/submission/
$ git clone git://github.com/dsv-su/moodle-assignsubmission_mailsimulator.git mailsimulator
As an administrator; go to Home > Site administration > Notifications to install the submission type.
MailSimulator is licenced under GNU GPL v3.
Copyright: Department of Computer and System Sciences, Stockholm University.