How to validate email on webform if the field type is textfield and you have data
After a couple days asking google for the solution, I did this.
1. Install the module  https://drupal.org/project/webform_validation
this will add another tab on your webform.
2. select "Regular expression, case-insensitive"
3. add the next regex (regular expresion)   ^[_a-z0-9-]+(.[_a-z0-9-]+)@[a-z0-9-]+(.[a-z0-9-]+)(.[a-z]{2,3})$
4. select your email field to validate and add some text to the error message.
that's it...
from now on all your email will be validate,  but the old data must be fixed by hand...
the good thing, is you do not need to migrate your data just for  fix it..

hopefully this will be helpful to someone...
 best