Email formalities

I'm currently writing an email to the Zentrales Prüfungsamt and I'm wondering just know how I should address them. I Have always used the "Sehr geehrte Damen und Herren" and then switch to "Sehr geehrte/r Frau/ Her...." and always with MFG at the end. I came to look for some advice or explanation and found this from an old post. What do you guys think about it?

Assuming they are female and named "Natalie Müller" and I am male and named "Max Mustermann":

If they replied "Sehr geehrter Herr Mustermann", I would stick to "Sehr geehrte Frau Prof. Müller"

If they replied "Lieber Herr Mustermann", I would switch to "Liebe Frau Prof. Müller"

If they replied "Lieber Max" and signed off with "mit freundlichen Grüßen, Natalie Müller", I would switch to "Liebe Frau Müller" (dropping the Professor, since they were also a bit informal with me)

If they replied "Lieber Max" and signed off with "liebe Grüße, Natalie", I would switch to "Liebe Natalie" (they basically offered first name basis by signing with their first name - it happens with young professors or very comfortable working environments)

There is nothing wrong with sticking with a more formal address if you want to be on the safe side, though. Unless you are looking to make a good impression (like if you want an internship). In that case being too formal can also be counterproductive if you come across as too stiff and a stick in the mud.