[fookyong]

Cool until I checked the source and realised that the developer has to hard-code a list of domains they want to check against (there are none included).

Off-the-shelf usefulness would be improved a lot if the plugin contained a list of say 100 or so of the most commonly-found email domains.

My 2c.

[mleonhard]

Here is the list they're using: http://kicksend.com/assets/splash.js

[vincentkriek]

It would be even cooler if it checked against MX records.