Exchange 2007; Restore mail flow from \"stuck\" queue

We have an 2008x64/Exchange 2007 server that is not delivering external emails nor is it inserting received external emails from the mail queue into the appropriate users' mailbox. Internal emails are working properly, and the system was working correctly until 2 weeks ago, when we believe some changes were made to the server by an ex-employee. We have already performed an eseutil /mh and p on the mail queue folder. These messages are hung in the queue with "430 4.2.0 STOREDRV; mailbox logon failure error". We have changed the user running "Exchange Transport" and "Transport Log Search" to Network Service, deleted the passwords, and restarted both services. We understand this is the common fix, but it has not caused the messages to deliver from within the queue. I even renamed the TransportRoles\data\Queue folder and recreated an empty queue to see if I could send/receive a test email that way but I didn't receive it, so I restored the original queue folder. I would like to recover these emails if possible but if not, I can delete them with an NDR and start over. I don't think this is the cause of the problem since a fresh empty queue also didn't work. We have used the MS Fixit Tool to set IPv4 as the default although we have left IPv6 installed and bound to our NIC. Because our Exchange 2007 server is also a GC, DNS, and Active Directory server we cannot remove this IPv6 binding otherwise the computer fails to start and it is very difficult to get the the server back online. Setting IPv4 and default allows the Exchange server to resolve itself via IPv4 when we ping it's NetBios name. We have run a eseutil /d and /p on the Mailbox EDB file and we have dismounted and mounted the "First Storage Group" via EMC to see if that would trigger delivery of the messages in the queue. We have set the Exchange External DNS servers to resolve using Google's public DNS servers, and we have tried using our own internal DNS servers to resolve. Nothing we do is causing the Mail Queue to empty or mailflow to work. I also occasionally receive messages that my HUB server and MAILBOX server aren't able to communicate (in Event Viewer) which seems to be the cause but as these are both on the same Windows installation and I can ping the NETBIOS name of the server, I'm unsure of what to do.