This is caused by a new spam fighting feature with Yahoo Mail called Grey Listing. For more details see this article http://en.wikipedia.org/wiki/Greylisting
What is happening is whenever a message is sent to yahoo, it replies with a "try again later message."
What it will do is wait for it to try again later if it likes the delay then it will allow the message to be sent.
What is happening is whenever a message is sent to yahoo, it replies with a "try again later message."
What it will do is wait for it to try again later if it likes the delay then it will allow the message to be sent.