Hey folks! So...I've been dealing with this issue for the past week, but haven't managed to find any solutions. I went through Apple's directions for fixing the problem: http://support.apple.com/kb/TS3276 but this didn't fix it. There is no indication why this happened, it didn't happen after an update, or something like that. I'm receiving message just fine, but I'm unable to send them. This is probably unrelated, but I've also been having issues with Flash...I'm essentially unable to watch anything on YouTube. I tried re-installing Flash, and while the DMG file is still open, YouTube worked for a minute or two (but has stopped working since). Again, probably unrelated...to be honest, though, I'm wondering if I have a virus? These are both pretty big issues.