Out of Office agent does not always send email to external emails such as yahoo, google, and hotmail. It will work for one employee and not another, there seems to be no rhyme or reason on why it works or does not work. Some users are set for 60 min and others 360, this still does not seem to effect if the message is sent out or not.
Check the user’s Tools - Out of Office settings under Exceptions tab. There is an option called ‘Do not automatically reply to mail from Internet addresses’.
Checked that they were allowed to send to Internet address–one of them even sent an email to google but not yahoo–actually none of them sent an email to yahoo.