I don't know how it is in the US, but in Europe, it would not be surprising to see a lot of student email address bounce back really quickly.
Students graduate, leave/change university, and the email system keeps only current students.
How else are you going to get hounded by your alumni association? I finally shook them after probably my 5th move out of college, then my Mom (of all people!) gave them my new address when they called her.