Stupid question: why don't they just offer to let Alumni pay for their content storage?
Professors, staff and registered students etc, on the other hand, is easier to deal with.
This could be done in perhaps the opposite direction: individual alumni donors tying donations to maintenance of email accounts for all alumni.
These email addresses, in some cases, must date back to the 90s or earlier. Cancelling them is a major, negative change to people who (like me!) who have come to rely on them.