When someone politely writes "I hope you are well" in an email, what is the proper response? I have two different levels of formality in mind:

1) Formal: We use each other's last names.

2) Semi-formal: I use their last name, they use my first name. Eg, a supervisor at an office job, or a professor I don't know very well.

Also, are there different responses for different variations of "I hope you are well"? For example, does "I hope this finds you well" require a different response?