You can use these methods to block any email extension and it can also prevent users to add URL in textarea field.

validate.js

// Block ru extention in email like www.google.ru
$.validator.addMethod("noRu", function(value, element) {
	return (this.optional(element) || value.slice(-3) != ".ru");
}, "The .ru extention is not allowed in email address");


// Prevent users to add any URL in textarea
$.validator.addMethod("noUrl", function(value, element) {
	return (this.optional(element) || value.match(/\b(http|https)?(:\/\/)?(\S*)\.(\w{2,4})(.*)/g) == null);
}, "URL is not allowed");