When sending tracked messages using PoliteMail, it is not necessary to use the Bcc field for your recipients.
Each recipient will get his/her own copy of the message addressed only to him/herself, even if they are on multiple distribution lists. No other recipients will be viewable. Sometimes the email address gets 'lost' when added to the BCC field and PoliteMail can not deliver it.
This causes it to get 'stuck' in queue.
For best performance, put all lists in either the To: field or CC: field.