That's a pretty good setup for alerts - but depends a bit on your trace interval. With 250 targets, you might also change your "Ping Timeout" to something a bit less than 9999 ms - just in case you have a bunch of simultaneous timeouts - with 9999 set, it will take a couple of minutes to wait through all the targets. Setting it to 1500 might be a bit better.

As for your alert events - the "Notify" dropdown on each alert event will let you pick "when alert conditions end" - which will make that event (an email in your case) happen when that target goes back up. Have another event on the same alert for "when alert conditions start" to get a notification when that target goes down, and then again when it goes back up.

- Pete