How do I access my zoho email with my iphone through POP?

How do I access my zoho email with my iphone through POP?

I have tried to connect my zoho email with my iphone and it looks like everything is in order.  I can receive messages, but it will not let me send any.  It keeps saying that "the sender address "my email" was rejected by the server.
 
Any help?
 
Thanks
Sean