How many @ symbol can be in an email address?

Question

Is there any rule for having a specified amount of @ symbol in any email id. Just come to my mind if we\'re to check if an email id is valid or not using PHP.

Answer 1

My real question is would it make sense to have two @ symbols in an email?
How would it work?

I would use filter_var() with FILTER_VALIDATE_EMAIL. Below is a sample use and outputs,

function testemail($email) {
    echo "'$email' => ";
    var_dump(filter_var($email, FILTER_VALIDATE_EMAIL));    
    echo "
";
}

testemail('');
testemail('myemailsample.com');
testemail('myemail@sample');
testemail('myemail@sample.com');
testemail('myemail@@sample.com');
testemail('myemail@sa@mple.com');

Output,

'' => bool(false)
'myemailsample.com' => bool(false)
'myemail@sample' => bool(false)
'myemail@sample.com' => string(18) "myemail@sample.com"
'myemail@@sample.com' => bool(false)
'myemail@sa@mple.com' => bool(false)