It is DEFINITELY a virus email (I am not 100% sure which one it is, but I believe it may be a variant of the NetSky virus Specifically, the P or Q variant. Click for details)
You need to take the necessary precautions on the server, and the machines of anyone who access the email. What you need to realize is that it may not be sent from anyone using your mail server. It is possible someone else who has your email address got the virus, and that virus found your email address in their inbox, and spoofed an email "from" your email address, so consequently when that mail went out, it bounced back to that email address.
The attachment triggers infection on the computer, so be sure not to try to open it. (An scr extension is a Screen Saver, but an scr is nothing more than an executable (.exe) with the extension renamed to .scr)