C# code to validate email address

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What about this?

bool IsValidEmail(string email)
{
    var trimmedEmail = email.Trim();

    if (trimmedEmail.EndsWith(".")) {
        return false; // suggested by @TK-421
    }
    try {
        var addr = new System.Net.Mail.MailAddress(email);
        return addr.Address == trimmedEmail;
    }
    catch {
        return false;
    }
}

Per Stuart’s comment, this compares the final address with the original string instead of always returning true. MailAddress tries to parse a string with spaces into “Display Name” and “Address” portions, so the original version was returning false positives.

To clarify, the question is asking whether a particular string is a valid representation of an e-mail address, not whether an e-mail address is a valid destination to send a message. For that, the only real way is to send a message to confirm.

Note that e-mail addresses are more forgiving than you might first assume. These are all perfectly valid forms:

  • cog@wheel
  • “cogwheel the orange”@example.com
  • 123@$.xyz

For most use cases, a false “invalid” is much worse for your users and future proofing than a false “valid”. Here’s an article that used to be the accepted answer to this question (that answer has since been deleted). It has a lot more detail and some other ideas of how to solve the problem.

Providing sanity checks is still a good idea for user experience. Assuming the e-mail address is valid, you could look for known top-level domains, check the domain for an MX record, check for spelling errors from common domain names (gmail.cmo), etc. Then present a warning giving the user a chance to say “yes, my mail server really does allow 🌮🍳🎁 as an email address.”

As for using exception handling for business logic, I agree that is a thing to be avoided. But this is one of those cases where the convenience and clarity may outweigh the dogma.

Besides, if you do anything else with the e-mail address, it’s probably going to involve turning it to a MailAddress. Even if you don’t use this exact function, you will probably want to use the same pattern. You can also check for specific kinds of failure by catching different exceptions: null, empty, or invalid format.

— Further reading —

Documentation for System.Net.Mail.MailAddress

Explanation of what makes up a valid email address

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