Customized Email Notifications Not Sent

We have a custom server-side event handler that sends customized project server emails when Assignments have been changed. The solution has been deployed to an environment but for some reason the customized emails are not being sent?

Does anyone have any good troubleshooting steps?

We checked the following:

1. The DLL is gac'd
2. DLL is the right version
3. Server-side event handler has the right settings
4. Event and Queue service timer jobs were re-started
5. Email notification server settings are configured
6. No errors in ULS or event viewer

Anyone have any other ideas?

Thanks!