Everyone seems to use a different one, and most of the regex you find online will fail the most basic email scenarios, due to inaccuracy or to the fact that they do not calculate the newer domains introduced, or internationalized email addresses Don’t use any regular expression blindly, but check it first.I made this example on Glitch that will check a list of email addresses considered valid against a regex.But what if I told you there were a way to determine whether or not an email is valid without resorting to regular expressions at all? The activation email is a practice that’s been in use for years, but it’s often paired with complex validations that the email is formatted correctly.It’s surprisingly easy, and you’re probably already doing it anyway. If you’re going to send an activation email to users, why bother using a gigantic regular expression?A complex regex validation on the email address doesn’t introduce an additional solution, it introduces an additional problem.We can validate email address at client side and server side.Here’s a fairly common code sample from Rails Applications with some sort of authentication system: If you’re experienced at Regex, this seems simple. Sections 3.2.4 and 3.4.1 of the RFC go into the requirements on how an email address needs to be formatted and, well, there’s not much you can’t do in your email address when quotes or backslashes are involved.If (like me when I first saw this) you AREN’T experienced at Regex, it takes a while to parse. The local string (the part of the email address that comes before the @) can contain any of these characters: is a valid email address. For this reason, for a time I began running any email address against the following regular expression instead: Simple, right? This is often the most I do and, when paired with a confirmation field for the email address on your registration form, can alleviate most problems with user error.
At this point, why keep parsing email addresses for their format?
Think about it this way: I register for your website under the email address . That’s probably going to bounce off of the illustrious mail daemon, but the formatting is fine; it’s a valid email address.
To fix this problem, you implement an activation system where, after registering, I am sent an email with a link I must click.
If the first character is a quotation mark, match a beginning quotation mark followed by at least one occurrence of any character, followed by an ending quotation mark.
While it's fine to check the format of an email address client-side using a regex, the only way to really, totally, be sure that an email address exists is to confirm that you can send email to it, and that somebody can receive it.