SirCAM does indeed act in a very advanced fashion.
The email address in the header above is of spanish origin and is most likely the effect of someone who has used either a website that contains your email addy (and the files are still in cache on their system) or a mailing list archive etc.
I've received 16 emails today, all infected with the same virus, of which 15 came from the same source. The header for that particular user was actually quite perplexing, as it originates from a server at leeds.ac.uk and yet is routed through a server in mexico (.mx) very strange! The other one came from an estate agents in Leeds, whom I telephoned and informed.
This particular virus, from what I've learnt from McAfee's virus information library;
gives the impression that although the virus is non destructive, it is still dangerous in the way it operates.
One additional piece of information about it though, is that the Subject line of the email will almost certainly be the filename of the appended file.
Unlike many other viruses though you should be able to hit reply and the reply does go back to the person who you received it from.
Best of luck!