We live in a world of interfaces like the one in the title picture. VBA also allows to use interfaces which offers a lot of possibilities. This article describes how to use interfaces in VBA and how to work around their bugs.
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions.
Consider email address RFCs:
Look at HTML5 form input element (with type=email) regex pattern: