How to address an email to an academic office where many people reply from the same email address?

I would reply to whoever wrote the latest email... it is a reply after all. When other people take over and respond, I interpret that as if the group that monitors the email is always in bbc, and is free to join in the conversation/take over when it becomes useful. When I reply, it's to the last person to have "spoken," unless I need to address something specific a different person said, in which case I might write back to both (ETA: as in, "Dear Mr. Smith and Ms. Jones, " or "Hi Sarah and Michael, " matching their tone).

There was some talk in the comments of this question about etiquette in various countries. I'm from the US but have worked in Europe for four years, and I still would go with this strategy. I know German addresses combined with honorifics are notoriously more formal than other languages, but usually when the conversation is in English and among an international crowd, the international English standards take over. I've never lived or worked in Germany, but get communications from German academics and haven't noticed any deviations from that norm.

The customary formal address in written English to an unknown (number of) recipient(s) is "Dear Sir or Madam". In German, it would be "Sehr geehrte Damen und Herren".

However, although German etiquette is a tad more formal than US etiquette, it's alright to just omit the salutation after the first or second reply in an email exchange.

Some other okay options, in order of my subjective sense of appropriateness (with 10 years in German and Austrian academia):

• "Dear Mr A, dear Ms B, dear Ms C"
• "Dear X" (with X being the person who replied last)
• "Hello"

"To whom it may concern" is not a great choice. It's very formal, old-fashioned, and used only when the recipients are unknown.

• To whom it may concern
• Dear sir/madam
• ...

Are fine for first contact. Subsequently, respond inline, which doesn't require a salutation.