In the pre-smtp days, email links were over UUCP, which was often relayed via dial up lines which connected intermittently, on a schedule (e.g. every hour).
Add in the situation of disk quotas for university students, but not email quotas, and you get the means, motive and opportunity for people to use the email spools of a mail servers around the world as an annex to their home directory...
You also specified not just the destination, but also the route for the email to take, via a 'bang path': https://en.wikipedia.org/wiki/UUCP#Bang_path
Add in the situation of disk quotas for university students, but not email quotas, and you get the means, motive and opportunity for people to use the email spools of a mail servers around the world as an annex to their home directory...