In Joomla 3.0.3 the email validation was changed in order to comply with html5 standards and to allow for longer top level domains (such as travel). As part of the change, top level domains are no longer required since they are not part of the standard for email names. When present they must be at least two characters long. Developers can use the TLD attribute to require use of a TLD. Please see JFormRuleEmail documentation for more detail.