Editable Gridview From List With Validation

I would like to be able to edit one field in a list on a SharePoint page in SP 2010 with SPD 2010. I cannot take the Visual Studio route to create the gridview and edit it. 

I have tried to add a datasource and link it to a gridview. But clicking Edit doesn't save the changes for whatever reason. My boss wants something like a gridview interface and the ability to edit an email address, but the email address has to be a valid email. 

I have programmed in Visual Studio for a number of years, but never in SPD against SP. 

What is the best method to attack this problem?