[pm215]

I think that last one isn't a modern standard email address -- the domain part is reversed. It's a JANET NRS path (https://en.m.wikipedia.org/wiki/JANET_NRS). The modern equivalent would be [e-mail].

The first email address (the ARPA one) is presumably using a machine in UCL as the gateway between internet routing and JANET routing, since the part before the % is the JANET NRS component ordering. The obvious conclusion would be that the mail server he was using didn't have an ARPAnet connection at all.