Are you receiving other types of events correctly?
Have a look at the eventparser.log on the ePO server - are there any errors? Feel free to attach a copy here if you like...
I have the same issue in two different ePO servers.
In eventparser.log I have only succeded events. Now I check if event ID 1284 was correctly parsed.
I had an issue with HIPS being installed on my ePO server and blocking the emails being sent (although the test one worked fine).
When I disabled HIPS all my emails came through that I was expecting.