When the amount of time it takes to process the notifications exceeds the notification wait time, it is possible for no notifications to be sent. When this happens it’s best to increase the notification wait time (Admin >> Server Settings >> Preferences >> Notification Wait Time (in seconds) then restart Agile.
From any object in Agile you can send via the Action menu Send selection. You can also test sending an email be directly connecting to the smtp gateway via telnet and sending a message the way Agile would using email commands. This is more cryptic but tests the smtp gateway and removes Agile from the equation. See attached pdf for how to run telnet and send email commands.