>His email address is at Earthlink, and if he is using Earthlink's SMTP server, I highly doubt that is the problem. They are one of the larger ISP's, and as far as I know, go to great lengths to prevent SPAM from bouncing through their servers...

The larger the ISP is, the bigger the chance they could be blacklisted as they have tons of users who can use their SMTP server to send email before they even notice it. Basically, it's really simple. Anyone can verify if a specific server is listed or not to the top spam blocker servers. If they are not listed, then the problem might have been a bad connection. However, from what was reported to me, the message received was the same as when it is blocked from our server. So, that's why I assumed it was the case.