Sometimes I would send an e-mail to an alum (to their work e-mail), and then receive a delivery failure notification. However, I'm pretty sure I got the e-mail right. My guess is that the person I'm trying to contact no longer works there.
When you look at LinkedIn, how do you figure out if the person's not there anymore? If they are almost 3 years into their analyst/associate program, is it a safe bet to say they are not there anymore (especially in the current economy)? Some people don't update their LinkedIn as frequently and I need to figure it out based on the information I have available.