Hi Rob,
In general, there could be three scenario where a delivery is in start pending stage.
1. The mta is not started and hence the delivery is not picked up for further processing. Nlserver monitor missing command can provide you a list of missing processes and nlserver pdump command shows running process. You can use them to see if mta is started
2. The affinity defined for this delivery is not present or correctly configured in the config file. To check the affinity currently used , open the delivery, click edit and click view xml source. Under the scheduling tag you can find the ip affinity.
3. The contact date for delivery is on future and will start on that date &time
Regards,
Adhiyan