That's odd...

I just recieved the most unusual piece of spam. HTML formatted, but all it contained was a plaintext three-digit number inside html and body tags. The subject was likewise just a (different) three-digit number. The sender was, supposedly, me. The actual point of origin is apparently a server on material.com, running SonicWall. The number combination is not a username and password on this server as far as I have been able to determine. Looking at the source-code shows nothing apparently unusual. I'm kind of stumped. There's not even an attachment. What kind of spam is this?