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.

Business Optimizer

rajivlodhia

A very simple plugin that turns your email address into a shortcode. This plugin provides a field and shortcode for your email address allowing you to use it anywhere on your site. If you ever need to update your email address, you’d just need to change it in one place.
This plugin works together with other Optimizer Shortcodes plugins. Find a list of all our Optimizer Shortcodes plugins <a href="https://businessoptimizer.org/collections/plugins" rel="nofollow ugc">here</a>.
<h3>Usage Instructions</h3>
After setting your email address in the new settings page (<code>/wp-admin/admin.php?page=optimizer-shortcodes</code>), you can use the shortcode [optimizer_email] anywhere on your site to display that email address. 
If you need to use the field value in your theme files or template, you can print it with PHP like this:

<h3>Credits</h3>
Plugin built by <a href="https://rajivlodhia.com/" rel="nofollow ugc">Rajiv Lodhia</a> for <a href="https://businessoptimizer.org/" rel="nofollow ugc">Business Optimizer</a>

Optimizer Shortcodes – Email

A very simple plugin that turns your email address into a shortcode. This plugin provides a field and shortcode for your email address allowing you to …

Email Domain Checker for WP e-Commerce vs Optimizer Shortcodes – Email