Check if an email address is valid

There are online tools that are available which allow you to check whether an email address is valid.  One such tool can be found at http://verify-email.org - simply enter in the email address and click on 'verify' and it will check to see whether the email exists.

This will not always be 100% accurate, as some email providers block the use of these validation tools - some government email addresses will always be returned as invalid, even when the email exists - but this will give you a fairly good indication of whether an email address if valid.