Vishal Kothari

This plugin validates the existence of the domain name that is entered in the email address while checkout. This plugin strengthens your email validation by more than just the regular expression matching, thereby reducing chances of loosing an order due to incorrect email address & increasing accuracy of your data.
The checkout process cannot be completed till the email address is entered with the correct domain, thus eliminating any chances of a wrong email address (at least the domain can’t be wrong).
If the domain is not a valid domain, it will show an error and not allow the customer to checkout till the email address is entered with the correct domain.
Other free plugins for WP e-Commerce:
<ul>
<li><a href="https://wordpress.org/extend/plugins/viral-coupon-for-wp-e-commerce-lite" title="Viral Coupon Plugin" rel="ugc">Viral Coupon Lite for WP e-Commerce</a> – Social Media Promotion Tool for your store (Facebook)</li>
<li><a href="https://wordpress.org/extend/plugins/order-delivery-date" title="Order Delivery Date" rel="ugc">Order Delivery Date</a> – Allow customers to choose their order’s delivery date</li>
</ul>
Premium plugins for WP e-Commerce:
<ul>
<li><a href="http://codecanyon.net/item/viral-coupon-for-wp-ecommerce/2644621" title="Viral Coupon Pro" rel="nofollow ugc">Viral Coupon Pro</a> – Promotes your store on Twitter & Google+ in addition to Facebook.</li>
</ul>

Email Domain Checker for WP e-Commerce

This plugin validates the existence of the domain name that is entered in the email address while checkout for WP e-Commerce store owners.

Nerd Warehouse

Allow users to check domain name availability directly from your website. Availability is shown without redirecting users. With the use of widgets you can add the domain search to multiple locations on your website. You can also quickly check domain availability yourself using the admin dashboard widget. This plugin is multisite compatible and free.
WordPress Domain Search is powered by <a href="http://www.nerdwarehouse.com/" title="Best WordPress Hosting" rel="nofollow ugc">NerdWarehouse.com</a>. Nerd Warehouse is a low-cost domain registrar and hosting provider that specializes in <a href="https://www.nerdwarehouse.com/products/wordpress" rel="nofollow ugc">WordPress Hosting</a>. Data centers in the United States, Europe, and the Asian-Pacific support our massive cloud hosting network and we offer localized 24/7 phone support.

WordPress Domain Search

This plugin allows you to create domain search widgets and check domain availability from the admin dashboard.

Email Domain Checker for WP e-Commerce vs WordPress Domain Search