WP SMTP Email sending Issue

I am facing issue in wp smtp plugin .The email is being sent to all of the domains(like yahoo gmail). But when I add info@abc.com.pk as a recipient’s email address then the contact form gives an error after submission of the form 😕 .Please help me ASAP.

Here is the plugin I am using in my website:

http://wordpress.org/plugins/wp-smtp/

Thanks