Have they done enough?

Yes, just about

Looking carefully, you manage to find small puffy white blebs on each of the four soles displayed in front of you that prove the intensity of the strapping the girls gave themselves. Pleased, you put the second part of your punishment into operation.

"Very good. Now, get dressed and head down to the Porters' Lodge to offer your help delivering the pigeon post. Tell them that you're available until lunch and ask them to make a note of the time you're despatched so the recipients can punish you if you're slow. Once you're dismissed, you may consider your punishment over, but woe betide you if I see you here again this year."

The students thank you profusely and hurry to obey, returning the straps they used on the way. The darker of the two hesitates, before asking whether she can tip you and you see the horror on her companion's face at the thought that she might have missed out this important aspect of being punished, but since you didn't administer the spanking personally, you don't feel a tip is necessary, much to their relief.

After they hobble out, trying rather unsuccessfully to glide elegantly on their terribly tender tootsies, you pack up your things, ready to head out yourself. The porters will use the girls to deliver packages all over the university, reducing the pressure on the overworked university courier service and getting the packets to their destinations sooner in the process. No great hardship, apart from having to clock up several miles in a morning upon feet that have already been strapped soundly. For all the technological advances that allow academics to communicate digitally, there never seems to be any shortage of things that need to be placed physically into a student's or staff member's pigeonhole, so you're sure there will be plenty of work and plenty of follow-up spankings if they slack off.