Sudden surge in spam appearing to come from my email address

[Thomas Cameron]

All -

I am suddenly getting hammered by a BUNCH of spam that appears to be 
from me. It scores low, and even though I keep feeding it to Bayes, it's 
still not hitting the threshold to be marked as spam.

When I check the headers, it's coming from multiple random email 
servers, but many appear to originate from hotmail/outlook.com. So from 
outlook.com, through some unsecured email server, then to my server.

I'm trying to figure out how to block this stuff. Something like "if it 
appears to come from me, but it's not actually coming from my email 
server," block it. I don't necessarily think this is a job for SA, but 
if there's a rule I can tweak or a setting I can change, I'm all ears.

Thanks,
Thomas