Has anyone noticed an increase in the amount of SPAM that has been getting past Spam Filter ISP?  Lately I have been seeing three similar emails slipping through.  They either have "check this.", "it's me.", or "wrote:" in the subject which changes every week.  The message is all text with no images and usually is about some tip about a hot stock.  I have been using the default filters and settings for the most part for about a year with relatively little spam getting through, but I have seen many of the SPAM messages I mentioned above getting through.  From what I can tell these messages are coming from IP addresses that aren't on any RBL lists and the domains seem to have valid MX records.  Is there any way to stop these messages besides using keyword filters which work for about a week until the message changes?

I also have been getting many complaints lately about an increase in spam.  We don't really run on defaults but for the most part about 2-3 hrs a week to stay on track with the spammers is what i spend tweaking.  This has however changed and I'm not sure why so many more are getting through.  The text only ones sometimes have links within them but they change periodically so what are the rest of you doing to combat?