Sometimes it is necessary to check if a mail is valid when a user is trying to register a new account on your website to avoid abuse. In addition to the format check, one more safety measure to take is to check if the email domain is a commonly used one to avoid some abuse. In this article I will illustrate how to do it using PHP.

Firstly, implement a utility class for mail addresses check.

<?php
class Check
{
    //
    public static function isEmailLegal($email)
    {
        return filter_var($email, FILTER_VALIDATE_EMAIL) && strlen($email) <= 32;
    }

    public static function isEmailMaiDomainCommon($email)
    {
        list($userName, $mailDomain) = explode("@", $email);
        $commonDomainList = array("gmail.com", "qq.com", "163.com", "yahoo.com", "hotmail.com", "outlook.com", "yeah.net", "live.com", "foxmail.com");
        return in_array($mailDomain, $commonDomainList);
    }
}

Then when checking if a mail is legal

// check email format
            if (!Check::isEmailLegal($email)) {
                $res['ret'] = 0;
                $res['msg'] = 'Illegal Mail';
                return $response->getBody()->write(json_encode($res));
            }

            // check mail domain
            if(!Check::isEmailMaiDomainCommon($email)) {
                $res['ret'] = 0;
                $res['msg'] = 'The mail domain is too unique!';
                return $response->getBody()->write(json_encode($res));
            }

Basically, it checks if a mail domain is inside a safe list, one like the commonDomainList in the above example.

References

1. https://stackoverflow.com/questions/19522092/should-i-use-filter-var-to-validate-email#answer-27384001