How to check for a duplicate email address in PHP, considering Gmail ([email protected])

Question 1

How can I check for duplicate email addresses in PHP, with the possibility of Gmail's automated labeler and punctuation in mind?

For example, I want these addressed to be detected as duplicates:

         [email protected]
        [email protected]
   [email protected]
  [email protected]

Despite what Daniel A. White claims: In Gmail, dots at random places before the '@' (and label) can be placed as much as you like. user.[email protected] and [email protected] are in fact the same user.

Question 2

$email_parts    = explode('@', $email);

// check if there is a "+" and return the string before
$before_plus    = strstr($email_parts[0], '+', TRUE);
$before_at      = $before_plus ? $before_plus : $email_parts[0];

// remove "."
$before_at      = str_replace('.', '', $before_at);

$email_clean    = $before_at.'@'.$email_parts[1];

Question 3

First, these are not variables, but constants.

And you can check their existence by using the defined() function :

bool defined ( string $name )

Checks whether the given constant exists and is defined.

Question 4

Using regular expression to validate emails is tricky

Try the following email as an input to your regex ie:^[w.-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,6}$

[email protected]

You can read more about email regex validation at http://www.regular-expressions.info/email.html

If you are doing this for an app then use email validation by sending an email to the address provided rather than using very complex regex.

Question 5

There is: is_uploaded_file(). When dealing with uploaded files, you should always use it (and its cousin move_uploaded_file()) for security reasons.

Question 6

are there any edge cases where a valid email address could fail an MX lookup check?

Yes, in that where there is no MX record, MTAs fall back to using the A record instead. So only allowing MX records would fail a class of mail servers that work in the real world.

Allowing any name with an MX or A record at least detects obvious mistypings that result in NXDOMAIN. However it will still allow mistypings that end up at squatter sites. A further step for addresses resolved by A records might be to check where port 25 is accepting connections on that address.

How to check for a duplicate email address in PHP, considering Gmail ([email protected])

Answers

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