Below code shows validation of Email address  use FILTER_VALIDATE_EMAIL flag

FILTER_VALIDATE_EMAIL - Confirms whether the value is a valid email address.  Generally, this verifies email addresses against syntax in RFC 822, except that whitespace comments and anonymous domain names are not supported.


$email =  "";
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
   $emailErr = "Invalid format and please re-enter valid email"; 

Above the syntax will verify whether the given email address is correct or not. If not, it will show an error message.