Use the following key to centrally manage the regular expression used for email address validation throughout the E-Commerce pages substituting the regular expression you want for your situation:

 

Site Admin Panel > Guest Related Settings > emailRegEx value = ^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zAZ][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$

 

If present in the site config file, it overrides any other regular expressions that are used for email address validation in the following files: Email.ascx, Checkout.aspx, Checkout2.aspx and Guestlookup.aspx.