Several folks at BBN worked on MMDF as well, often as part of the CSNET
project which BBN ran.* I always thought the five control-A's were a
failure of imagination (never going to send binary?). MMDF's biggest
failure was synchronous sending -- if you made a typo in an email address
the mail UA would bring it back to edit-mode -- which didn't work for
store-and-forward mail configurations.
Steve Bellovin had a funny quip about CSNET and Usenet, comparing
professors applying for NSF grants and grad students just setting up modems.