3

There is way to detect whether an email id is well-formed or not. Example abcqs@def.com is a well-formed email address, but this may or may not be valid email account.

  • Case 1 May be the domain doesnot exist (e.g. def.com here).
  • Case 2 If the domain is valid then may be the id doesnot exist for the domain (eg abcqs username doesnot exist for def domain).

If it is not valid then if we sent mail, we will get some delivery failure mail, maybe in some hours after sending the email.

I want to implement a similar concept. I want to verify if an email id belongs to a valid account, which will find out whether the account exists or not.

How to achieve it?

Visruth
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    Can you clarify your question? You seem to understand that although you can rule out various aspects of an email address as being *invalid*, you can't be sure it's *valid* until you send to it. So what are you asking? How to implement an email verification system? – T.J. Crowder Jul 26 '11 at 14:27
  • If I understood, he wants to verify if one email is valid when he creates an account. So, yes, your last question is correct: an email verification system. – woliveirajr Jul 26 '11 at 14:37
  • @T.J.Crowder, I am interested to know about how to implement email verification system –  Jul 26 '11 at 14:39
  • do you want to make a program which works like in this given link http://verify-email.org/ ? – Visruth Dec 14 '12 at 05:40

6 Answers6

5

I think a better approach is to send an email and verify it the user activates the account.

  1. The user fills in his email
  2. You create a link to be acessed by the user, passing some parameter to him. Example: http://your.domain.com/activate?account=984239048302948203482390
  3. You save the email and all info in your database, with a flag (a field) indicating that it hasn't being activated yet, and the code you sent him
  4. When he clicks the link, you'll receive that parameter in your site, in some program you have wrote. So you'll know that the parameter 984239048302948203482390 has been used
  5. You verify if that code exists in your database and activate the account.

And them he's verified.

You can check your database, every x days, and remove all the old entries, like one that weren't validated more than one week ago.

woliveirajr
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4

Unfortunately, you cannot know if it's valid until you actually send the message, as it's the remote server that decides whether or not the address is valid. All your local computer knows how to do is route the message to the appropriate domain for processing.

You could check to see if the domain name resolves if you wanted, but you still wont know if the exact email address exists.

Nick
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  • Indeed. There are various ways you can know that it's *invalid*, but you can't know it's *valid* until you send to it. But I think it's clear from the question that the OP knows that (what's *not* clear is what they want us to help them with). – T.J. Crowder Jul 26 '11 at 14:27
  • Well getting into details, the SMTP protocol sort of allows this, but because of the way the protocol works, its an identical to just sending an email, as the attempt will err out before any message content is streamed across anyway. – Nick Jul 26 '11 at 14:31
3

As Nick posted, you can't really know for sure until you send it. However, you CAN check against MX records for the given domain name programmatically: http://stefanp.eu/blog/2009/09/dns-lookup-mx-records-java/ . This solves your case-1

HTBR
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2

Validating emails has been discussed many, many times on SO. In short there is NO WAY to know whether an email address/inbox actually exists. Some servers may helpfully bounce an email addressed to a non-existent inbox, but many/most will not.

Additionally regex validating of an email format is also pretty much a lost cause. It is is trade off between maximising coverage and minimising false positives. Plus of course there are genuine addresses that do not adhere to the various RFCs. So my advice is to do a simple sanity check: check for the existence of the "@" character.

If you want to validate a sign-up, include a link in the email that contains the user id and some random auth code. The user clicks this to authenticate his account. If he's given a bogus address he wont get the email, and his account will not be validated.

Community
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Richard H
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1

When you want to veryfy an email address, create a unique number and store it in a database against the email address. Then send an email to the address with a link back to your website. The link should have the unique number as a parameter. The email should say something like;

Click here to verify your email address.

Once your website receives a hit on the link with the given unique number, you know that the email address is real.

Qwerky
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0

(Voted up several of the other answers - agree that user email verification is probably best - but wanted to also contribute this simplistic version of DNS validation that Henri described. The link he posted requires another library, but you can do at least basic checks without it.)

Here's the basic domain check:

public boolean isValidDomain(String domainName)
{
    try
    {
        InetAddress.getByName(domainName);
        return true;
    }
    catch (UnknownHostException e)
    {
        return false;
    }
}

And here's the basic DNS MX record check:

public boolean isValidEmailDomain(String domainName)
{
    try
    {
        DirContext ictx = new InitialDirContext();
        Attributes attrs = ictx.getAttributes("dns://" + dnsServer + "/" + domainName,
                                              new String[] { "MX" });
        Attribute attr = attrs.get("MX");
        return (attr != null);
    }
    catch (NamingException e)
    {
        return false;
    }
}

Where dnsServer does not have to be used in some environments, but will have to be in others. You may need to experiment there.

(All classes referenced are in java.net or javax.naming.)

dbreaux
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