$contact->do_not_email is always null

In function phplist_process_queue() , $contact->do_not_email is always null

$contacts = phplist_get_contacts($group); does not return this value.

You have to add

$contact2 = crm_get_contact(array('email' => $contact->email));

and then change every instance of $contact->do_not_email to $contact2->do_not_email

or something like that.