Sounds like you've got the opposite problem then, might make sense for your department manager to unassign tickets for people who are leaving for the day, I'm under the impression that they'd be letting someone know when they go.
The problem with getting an email every time someone claims a ticket would be that you'd rapidly learn to ignore them.
It would just happen all day, who would want to remember all of them?.. when it could do it for you!
We'd have to change it to email on claim anyway, so maybe a more efficient change would be better.
Maybe you mark tickets that are claimed but the agent who had claimed it is no longer active in a different colour? Let the system keep track, but with a gap long enough for lunch etc.
For instance, if you've made no actions or page loads for 30m, the system could simply drop your claims, it could increase the priority, change the SLA, assign someone else or the whole team.. likely a simple change of colour would be enough though.
It may be a little naive to do just that though, it would drop all claims overnight or weekend etc.. hmm.
Maybe we detect the number of concurrent sessions, if more than one, we can assume it's work time and then start changing things for assigned tickets with an agent who isn't signed in..
Have a think mate, if you're still sure getting an email every time someone claims a ticket is the way your team would work best, I'll have a look and tell you what you'd need to change to get that to happen.