VBA For MS Access 2010 - Checking For Valid Email Only When An Email Is Entered?

Here is the problem, I have an Access form and a textbox for an e-mail address. The email address is not required, I only want to check for a valid email address when a value or address has been entered into the e-mail filed. Example: If e-mail is not empty or if email field has a value, then check for the follow elements, matched the email address with the required format. If the e-mail field is empty, do not look for anything, move on.