PHP check email email function (strange writing method)_PHP tutorial

A PHP form email sending program I wrote before, in which the following method is used to verify whether the email address format is correct:

The code is as follows Copy the code
eregi("^[_a-z0-9-]+(.[_a-z0-9-]+)*@[a-z0-9_-]+.[a- z0-9_-]+.*", $email)

It was later discovered that email addresses similar to . mistakenly written as , could also pass verification, such as user@126,com. After checking, I found that it actually only verified the username part, so I found a tutorial online with the following example:

The code is as follows Copy the code
eregi('^[_a-z0-9-]+(.[_a-z0-9-]+)*@[a-z0-9-]+(.[a -z0-9-]+)*$',$email)

After checking, it was found that the email address user@126,com was still able to pass its verification. Found an example:

The code is as follows Copy the code
eregi("^[_.0-9a-z-]+@([0-9a-z][0-9a-z-]+.)+[a-z]{ 2,3}$",$str) www.111cn.net

This one looks more reasonable because it validates the suffix name. Although there are now top-level domain names with more than 4 characters, it only needs to be slightly modified. However, the email address user@xxx,com 111cn.net can still pass the verification. After careful inspection, it was found that it was because the . was not escaped. So I modified it slightly:

The code is as follows Copy the code
eregi("^[_.0-9a-z-]+@([0-9a-z][0-9a-z-]+.)+[a-z]{ 2,4}$)

It seems to be working well for now, although it is a bit more lenient in checking usernames.

Example 1

Copy the code as follows
function is_valid_email($email, $test_mx = false)
{
if(eregi("^([_a-z0-9-] +)(.[_a-z0-9-]+)*@([a-z0-9-]+)(.[a-z0-9-]+)*(.[a-z]{2,4} )$", $email))
if($test_mx)
{
list($username, $domain) = split("@", $email);
return getmxrr($domain , $mxrecords);
}
else
return true;
else
return false;
}
?>

Example 2 (written by myself)

Copy the code as follows
function is_valid_email_address($email){
$qtext = '[^//x0d//x22//x5c//x80-//xff]';
$dtext = '[^//x0d//x5b-//x5d//x80-//xff]';
$atom = '[^//x00-//x20//x22//x28//x29/ /x2c//x2e//x3a-//x3c'.
'//x3e//x40//x5b-//x5d//x7f-//xff]+';
$quoted_pair = '/ /x5c[//x00-//x7f]';
$domain_literal = "//x5b($dtext|$quoted_pair)*//x5d";
$quoted_string = "//x22($qtext| $quoted_pair)*//x22";
$domain_ref = $atom;
$sub_domain = "($domain_ref|$domain_literal)";
$word = "($atom|$quoted_string)";
$domain = "$sub_domain(//x2e$sub_domain)*";
$local_part = "$word(//x2e$word)*";
$addr_spec = "$local_part//x40 $domain";
return preg_match("!^$addr_spec$!", $email) ? 1 : 0;
}

For more details, please check: http://www.111cn.net/phper/php-cy/57193.htm