I found this questions asking how to do this in many different forums, so I will describe here how to implement a solution using PHP and AJAX.
The logical flow for the problem should be:
Write an event handler for the first drop down box to get …
Have you tried to learn about Unicode, UTF-8, and multibyte text encoding and all the articles are just too "academic" or too technical? This article aims to make the whole topic easy for just about anyone to understand.
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: