Change the default validation for the Emailaddress

Hi,

we want to use a custom validation for the Mailaddress field overwriting the default validation. We are using a Javascript with a  regularexpression Onchange which allows the following mailadress:

xyz-@test.de (^[a-z0-9!#$%&'*+\/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+\/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$)

Because of the Mailformat-Setting for the field, everytime we enter the address, we get the default error.

We don't want to create a new field (without Mailformat) but want to use the old field.

Many thanks