Name: distrocar
E-mail: ...
Website: ...
Country code: US
IP address: 110.136.161.73
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.10) Gecko/20100915 Ubuntu/10.04 (lucid) Firefox/3.6.10 GTB7.1

... OK so maybe user agent isn't reliable.  Maybe they bounced through some windows host to deliver the spam, I can't prove it really was a Linux box...  But I can say that user agent claims to be FireFox running on unbuntu, and posted spam.

Note: I flipped our DKIM signatures to production; mail to Yahoo, Google and others that support DKIM should now indicate (somewhere) that the DKIM matched.  On Google, it appears underneath the normal headers.