I have set up my iPhone with the new Yahoo server - I cannot send an email to myself - it thinks my own email is invalid

I cannot seem to send myself an email from my iPhone Mail app ever since my comcast email was switched to the Yahoo SMTP Server.  I can succesfully send email to anyone else except to the same email account (my own). When I do, it bounces back with "Cannot Send Mail. "username@comcast.net" and "username@comcast.net" are not valid email addresses and have been rejected by the server."  But they ARE my email address.  So how do I fix this issue?