I believe you are asking about grey listing The issue that you are experiencing should not be related to grey listing. Gray listing is when a mail server is configured to 4xx defer the first connection from a mail server that has not connected to it before. This is considered to be an "anti spam" measure by some people since a legitimate mail server will try to resend email again later and an incorrectly configured mail server and some spam programs will not bother to try sending the message again.
Can you copy and paste the exact and entire error message into this thread? I'd like to see exactly where and when the problem is occurring. Is it possible that Yahoo is allowing you to send the email, but that the person you are sending it to is not able to accept emails that big?