<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
	backgroundColor="#FFFFFF"
	backgroundAlpha="0"
	xmlns:me="com.mycustom.components.*">

	<mx:Form>
             <mx:FormItem label="Email Address:" >
		<me:TextInputEmail />
             </mx:FormItem>
             <mx:FormItem>
		<mx:Button label="Submit" />
             </mx:FormItem>
	</mx:Form>

</mx:Application>

package com.mycustom.components
{
    import mx.controls.TextInput;
    import mx.events.ValidationResultEvent;
    import mx.validators.EmailValidator;
    import flash.events.Event;
    import mx.validators.ValidationResult;

    public class TextInputEmail extends TextInput
    {
        private var emailValidator:EmailValidator = new EmailValidator();
        private var validator:ValidationResultEvent;

        public function TextInputEmail()
        {
            super();
            this.emailValidator.source = this;
            this.emailValidator.property = "text";
            this.addEventListener("enter", this.validate);

        }

        private function validate(event:Event):void
        {
            validator = emailValidator.validate();

            if (validator.type == ValidationResultEvent.VALID)
            {
                this.errorString = "";
            } else {
                this.errorString = validator.message;
            }
        }
    }
}