Most likely, the message that you sent was queued up on the University's e-mail server that was unable to deliver it to the intended recipients because of some problems with the recipient's e-mail server. A typical e-mail server is configured to try to deliver an e-mail message for a specific period of time, most often 4 days. If the problem that prevented the server from delivering your message has been addressed within that period of time, then the message will be delivered successfully but with some delay. If however, that problem still exists when the "retry" time interval expires, them message gets returned to the sender with a "Delivery time expired" message.