Sorry, I don't know if I can be of any assistance. If you have a failure to send mail, that doesn't mean it YAF is failing to send. I would guess your webhost is failing to send, or perhaps there is a username or password or port that is incorrect?
Using the credentials you put in your mail.config, can you log into that account, send an email and receive an email? This test will verify the account can send and receive.