Have you seen what your array holds? I'd change
$recipients_array = array($rowmq2->email);
to
$recipients_array[] = $rowmq2->email;
Then before going any further, run a foreach loop to print out the values of $recipients_array and make sure it has all the values
foreach($recipients_array as $value) {
echo $value . "<br>";
}
If the array is structured properly, then proceed to run implode()
Cgraz