There's a VERY rough reverse-engineering of it in the mail part of DECnet for Linux. I didn't document it, sorry, because I was implementing it as I went. But it might be helpful to you. http://linux-decnet.cvs.sourceforge.net/viewvc/linux-decnet/dnprogs/mail/ Chrissie On 20/06/2012 11:27, Sampsa Laine wrote: Does anyone have an outline of how the MAIL-11 protocol works? Toying with the idea of writing a Python library to send MAIL-11 messages using the DECNET-linux stack.. Sampsa