To view the raw delivery logs of a clean message, from the Quarantine+ page, select the "All clean mail" option, enter a string from either the From or Subject line of the message:

 
Once you have located the message that you want to view the delivery logs on, click on the "Troubleshoot" option located below the message:

 
You can then click on the "was not received" button for an explanation of what happened to the message, or "View full delivery logs" to see the full log:

When viewing the full log, in the case that more than one delivery attempt has been made, a list of delivery logs will be presented so that you can view the logs on previous delivery attempts.
 
See also: Tracking down a message after it has been delivered to your mail server