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.

cgarvey

This plugin lets you use a shortcode to automatically generate ‘cloaked’ email addresses in your content.
What is cloaking? 
Take an email address like barack@whitehouse.gov. If that was to appear on one of your posts/pages, it could easily be ‘scraped’ or ‘harvested’ automatically to add that email address to a spam list of some sort. Cloaking is all about making that harder to do.
How does this plugin do its cloaking? 
For any email address you include in your content, using the custom shortcode of [email barack@whitehouse.gov], that email address will appear as “barack -at- whitehouse -dot- gov” in your content initially. JavaScript running in the browser will then convert that email address to a regular, clickable, email link. Whilst it may seem pointless to convert a regular email address to a strange format only to convert it back again, the idea is that most automated ‘scrapers’, or ‘harvesters’, do not run JavaScript and hence won’t be able to pick up on the non-standard email address. The vast majority of users visiting your site will have JavaScript, and will see regular email addresses (not the strange format).
What about users who have no JavaScript, or have it disabled? 
They will see the strange format (“barack -at- whitehouse -dot- gov”). You can include a footnote using a custom short code [emailnojs] which will explain the strange format, if you wish to cater for that tiny minority of visitors.
<h3>License</h3>
This plugin uses the GPLv3 license.

Email JavaScript Cloak

A simple plugin to use JavaScript to cloak email addresses in your WordPress content (posts & pages).

Email Domain Checker for WP e-Commerce vs Email JavaScript Cloak