Verify email in Java

Question

Is there any way to verify in Java code that an e-mail address is valid. By valid, I don't just mean that it's in the correct format (someone@domain.subdomain), but that's it's a real active e-mail address.

I'm almost certain that there's no 100% reliable way to do this, because such a technique would be the stuff of spammer's dreams. But perhaps there's some technique that gives some useful indication about whether an address is 'real' or not.

Answer 1

Here is what I have around. To check that the address is a valid format, here is a regex that verifies that it's nearly rfc2822 (it doesn't catch some weird corner cases). I found it on the 'net last year.

private static final Pattern rfc2822 = Pattern.compile(
        "^[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$"
);

if (!rfc2822.matcher(email).matches()) {
    throw new Exception("Invalid address");
}

That will take care of simple syntax (for the most part). The other check I know of will let you check if the domain has an MX record. It looks like this:

Hashtable<String, String> env = new Hashtable<String, String>();

env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");

DirContext ictx = new InitialDirContext(env);

Attributes attrs = ictx.getAttributes(domainName, new String[] {"MX"});

Attribute attr = attrs.get("MX");

if (attr == null)
    // No MX record
else
    // If attr.size() > 0, there is an MX record

This, I also found on the 'net. It came from this link.

If these both pass, you have a good chance at having a valid address. As for if the address it's self (not just the domain), it's not full, etc... you really can't check that.

Note that the second check is time intensive. It can take anywhere from milliseconds to >30 seconds (if the DNS does not respond and times out). It's not something to try and run real-time for large numbers of people.

Hope this helps.

EDIT

I'd like to point out that, at least instead of the regex, there are better ways to check basic validity. Don and Michael point out that Apache Commons has something, and I recently found out you can use .validate() on InternetAddress to have Java check that the address is really RFC-8222, which is certainly more accurate than my regex.

Answer 2

You cannot really verify that an email exists, see my answer to a very similar question here: Email SMTP validator

Answer 3

Without sending an email, it could be hard to get 100%, but if you do a DNS lookup on the host that should at least tell you that it is a viable destination system.

Answer 4

Apache commons provides an email validator class too, which you can use. Simply pass your email address as an argument to isValid method.

Answer 5

Do a DNS lookup on the hostname to see if that exists. You could theoretically also initiate a connection to the mailserver and see if it tells you whether the recipient exists, but I think many servers pretend they know an address, then reject the email anyway.

Answer 6

The only way you can be certain is by actually sending a mail and have it read.

Let your registration process have a step that requires responding to information found only in the email. This is what others do.

Answer 7

I'm not 100% sure, but isn't it possible to send an RCPT SMTP command to a mail server to determine if the recipient is valid? It would be even more expensive than the suggestion above to check for a valid MX host, but it would also be the most accurate.

Answer 8

If you're using GWT, you can't use InternetAddress, and the pattern supplied by MBCook is pretty scary.

Here is a less scary regex (might not be as accurate):

public static boolean isValidEmail(String emailAddress) {
    return emailAddress.contains(" ") == false && emailAddress.matches(".+@.+\\.[a-z]+");
}

Answer 9

public static boolean isValidEmail(String emailAddress) {
    return emailAddress.contains(" ") == false && emailAddress.matches(".+@.+\\.[a-z]+");
}