A problem with SMTP

Hi all,
I am new to this group,
I have been working on an Open AT modem ,
I do have the problem of sending the Mail using yahoo,
But i can access the Mails using POP3

The Problem is that i get a #CME error 38016 each time i attempt a mail transfer ,
The SMTP port nuber is 587 ,i also tried using the port number 25 but did not get it working .
the other configurations are:
smtpserver: smtp.mail.yahoo.com

The above mentioned confiiguration was working fine untill last week ,but since then it is not for the same configurations mentioned above.

I doubt whether the server and domain settings have been changed for yahoo.

If any one do have suggestions in this regard Please do reply