I'm using OS 10.6.8 and Mail 4.6. My internet provider is Comcast and my email is through Fat Cow. So my email starts with Fat Cow, goes through Comcast and comes in through my POP settings. At the end of last week my email would no longer send from my computer. I receive everything, I just can't send. I spoke with Fat Cow and they said their settings were fine and could send and receive from my account. I called Comcast and they reviewed the settings and said it was either Fat Cow or my Mail software. Also, I have a laptop and iPhone with the account set up as IMAP, and can send just fine from the same email. I'm at a loss here! FYI, I don't want to change from POP to IMAP on this computer. Thanks for any help or ideas on this!