Hello Cemil,
Unfortunately it is not possible to determine if an address is really valid this way.
Usually messages are accepted by the server and if the address is invalid the messages are bounced later.
So for Yahoo the class is not very useful.
Take a look at this article to understand better how email validation works.
phpclasses.org/blog/package/13/post
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If you want to deal with invalid email addresses handling bounced messages, you may want to check this class:
phpclasses.org/package/9959-PHP-Han
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