What would cause email to not leave iService? There are no related log files in the website or mail popper folders.
The iService.MailPopper Windows service must be running for the system to send and receive email. As part of the upgrade process, this service is typically turned off (or removed if there is a DB update). So, if your system is not sending or receiving email but there are not error log files, this would be the first thing to check.
When the mail processor is not running all mail will be queued until it is turned back on. As soon as you restart the service all queued mail will be delivered and all mail waiting to be popped in your monitored mailboxes will be processed.