This is Part 6 of the CodeHousekeeping Series.

Code Housekeeping refers to general rules of thumb that make code easier to read, digest, and modify for other developers, yourself included.

Today, we will look at the issue of email address validation.

Every developer, myself included, has tried to be clever and attempted to validate an email address with a regular expression.

How hard can it be?

regex

A very comprehensive regex for email is this one:

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])

The trouble is that even this does not catch 100% of all valid email addresses, including many that appear to be invalid that are in fact valid.

Personally, I don’t bother at all and let the user enter whatever they want.

If the email is invalid, it will fail to send, and the mail server will respond with the appropriate error.

My logic is therefore “did you key in anything?”

But if I had to do it, I would do it this way:

using System.Net.Mail;

bool IsValid(string email)
{
    try
    {
        var addr = new MailAddress(email);
        return true;
    }
    catch
    {
        return false;
    }
}

Here I am using the MailAddress class in the System.Net.Mail namespace to do the validation for me.

If it fails, an exception is thrown, which I catch and discard.

TLDR

Email address validation is a hard problem, and not worth the bother of doing it yourself. But if you need to, don’t re-invent the wheel.

Happy hacking!