How to filter/remove Google Email ALIAS with PHP?

Question

I can create the unlimited email alias in Google Accounts (Gmail), ref: http://www.gizmodo.com.au/2014/09/how-to-use-the-infinite-number-of-email-addresses-gmail-gives-you/

But I need to filter email address to avoid that a user uses the same original email for the register in my application.

I would like to know if have anything to solve this? or my unique option is filtering with regex?

Nauseous

You shouldn't do this. There are many domains that use Gmail that you don't know are using Gmail. There are other reasons someone might have a + in their username. – Communicate

@Communicate Can I check if email domain are linked with Google Accounts? via DNS, eg – Nauseous

@Jonas Not reliably. A company can use Google Apps and still have some other SMTP server in front of Google. This isn't all that uncommon. A lot of companies will split their mail users between Google Apps and Exchange for example. This is a very common scenario during migration from something to Google Apps. – Communicate

Gave you an upvote on this question because someone downvoted it and my answer without explaining why. I think it's a valid question based on its regex merits. – Radiology

nice @tristan, thanks.... I consider this question important too, because some web application provide any service with unique email based, it must check this issue. – Nauseous

Answer 1

I don't agree with the comment outright stating that you shouldn't strip out the "filters" (e.g. [e-mail]). "Your use cases aren't the same as my use cases" and so on.[0]

tl;dr: The regex pattern you're looking for is: '(\+.*)(?=\@)'

Explanation:

To start, write a regex that matches the literal '+' sign and any single character, any number of times:

'(\+.*)'

When replacing this pattern with an empty string, this will turn [email protected] into tristan. If you decide to split on the @ symbol, congrats, concat the resulting string to '@' + domain.TLD to this and you're done. I mention this in case you've already split the e-mail address and it's just hanging around anyway.

If you're not splitting the user-email address on the @ symbol, you need to use a "positive look-ahead" (match this pattern if it's proceeded by this thing I specify) to tell your match when to stop (so we don't take away too much):

'(\+.*)(?=\@)'

with this in place, we get [email protected]. Hooray, that wasn't actually so rough.

---

[0]: In one of my applications, I store the original filter-containing e-mail address that users give me for communications, but track filter usage and consider the canonical account (referenced-internally) to be the version without the filter (e.g. [email protected]). I do this to make it easier for users that opt-in to be located by e-mail address to search for each other.

I understand why people use aliases/filters:

• they give the illusion that they can be used to track spammers (as if an e-mail harvester wouldn't remove the filter before selling a list)
• they're useful in routing emails or triggering events (e.g. sending a text when you get an e-mail from [email protected])
• the "omg i can do this?" factor

Which is all to say, "I get it, people like filters," but there's valid reasons as an application author or a company to make note of them.

Radiology

Edit: wow, why the downvote? This is a regex question and now it has an answer that works. – Radiology

About your [0] point: exactly, it's very easy manipulate a email list to remove the alias. – Nauseous

a new question: I can filter just email of Gmail's domains to avoid new registers with same email address real AKA without alias (duplicate email) on my web application, What's you think? .... PS: I says this, taking account the popularity of Gmail – Nauseous

New questions mean new questions on Stackoverflow, but for what it's worth, I only remove filters on gmail domains for my application because I know their rules (highly unlikely, but a different service might consider [email protected] to be a different account than [email protected]). If my answer helped you, mark it accepted. – Radiology

Answer 2

I wrote a function in php that I've been using to do this now too:

function unalias_gmail($email) {
    return preg_replace('/(\+[^\@]+)/', '', $email);
}

This will return the email address without the alias if it's there, or the given email address if there is no alias. I have a dataProvider for phpunit so you can see my tests:

<?php

require_once __DIR__ . '/path/to/helper.php';
use PHPUnit\Framework\TestCase;

class HelperTest extends TestCase
{
    public function data_test_unalias_gmail(): array
    {
        return array(
            // Provided email vs the expected result
            array('[email protected]', '[email protected]'),
            array('[email protected]', '[email protected]'),
            array('[email protected]', '[email protected]'),
            array('[email protected]', '[email protected]'),
        );
    }

    /**
     * @dataProvider data_test_unalias_gmail
     */
    public function test_unalias_gmail($email, $expected): void
    {
        $actual = unalias_gmail($email);
        $this->assertEquals($expected, $actual);
    }
}

Gives me a happy OK (4 tests, 4 assertions) =]

Note: This will need some love if they start allowing plus signs in domains!

Narrowminded