This question comes up fairly often. I would say that the validation framework should be extended to support this behavior, but I do not see the value.
The basic idea is that you have a form with fields...say Name and Email Address. If validation fails then the page is redisplayed with the values that the user entered. The user would then see validation messages like "Name is required" or "Email Address is not a valid email address". Putting the email address that the user entered into the validation message does not seem to add much value because the user can look at the Email Address field and see the value that was invalid. Also if you had multiple email address fields on your page the user would have to figure out which field is invalid.
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