How User ID became an E-mail Address

Hi All,

In our website portal, there is an E-mail address field and User ID field on registartion form. User ID field is editable and whenever user enters E-mail address, it is copied into User ID. A welcome mail is sent to user's email address entered during registration.

Now, some one entered E-mail address as and User ID as user. This user was not recieving E-mail notification.

After searching, we found that E-mail was sent to user instead of Woooowwwww, so user is recieving notification at User ID. This issue consumed time and it was a major issue.