I don't know much more about the transition - only that the professor is becoming the new head effective [date], and that they have the support of the department.
Do I send congratulations (because it's a promotion) or condolences (because apparently some professors don't actually want the promotion, and only become the head of department reluctantly)?
Edit: what about the outgoing head of department? I clearly shouldn't send condolences in that case, but should I send congratulations?
If you want to follow convention, congratulate the new head of department.
Again, if you want to follow convention, congratulate the outgoing head on his or her retirement.
– Robbie Goodwin Dec 24 '20 at 00:37