Remove all characters except letters, digits and !#$%&’*+-=?^_`{|}~@.[].

var_dump(filter_var('[email protected]', FILTER_SANITIZE_EMAIL));
var_dump(filter_var("!#$%&'*+-=?^_`{|}~.[]@example.com", FILTER_SANITIZE_EMAIL));
var_dump(filter_var('john/@example.com', FILTER_SANITIZE_EMAIL));
var_dump(filter_var('john\\@example.com', FILTER_SANITIZE_EMAIL));
var_dump(filter_var('joh [email protected]', FILTER_SANITIZE_EMAIL));

Results:

string(16) "[email protected]"
string(33) "!#$%&'*+-=?^_`{|}~.[]@example.com"
string(16) "[email protected]"
string(16) "[email protected]"
string(16) "[email protected]"