I can't send any emails on one of my email accounts in Apple's Mail application even though I can receive emails with this account. My other accounts send and receive. I have no problem sending from this account on my iPad or iPhone, so it's not the account, it's definitely the Mail application.
My wife is having the same problem on her Macbook with her Gmail account. I've deleted the Keychain entries for the accounts, and then entirely deleted the accounts and created them again -- neither worked.
I'm using a Macbook Pro running 10.8.3 with Mail version 6.3
Is anyone else having this problem?