Chances are your ISP is increasing its anti-spam efforts, to keep junk mail out of your inbox. I’m generally in favor anything that’s done to fight spam, but I’m just not sure about a solution at the ISP level. The technology is just not good enough yet that “false positives” (legitimate mail that is mistakenly identified as spam) don’t happen — this means that your ISP could be blocking your e-mail, and you would be none the wiser.