if (Ext && Ext.form.VTypes) {
		var email = /^([\w]+)(.[\w]+)*@([\w-]+\.){1,5}([A-Za-z]){2,4}$/;
		Ext.apply(Ext.form.VTypes, {
			EmailList: function(val) {
				var addrs = val.split(',');
				var idx = Ext.each(addrs, function(item) {
					return email.test(item.trim());
				});
				
				return !Ext.type(idx);
			},
			EmailListText: 'Not a valid email address or comma separated list of email addresses.'
		});
	}

Adding an ExtJS VType of EmailList

JavaScript