If the email were to be addressed to a specific person, you could write "Dear [Name]".
But is it appropriate to write "Dear [Team / Department / Company]"?
For example, "Dear Service Desk," and "Dear Microsoft,".
If it's within your own company you can use simply "Colleagues,". If specifically your own team, then "Team,". (i.e. no "Dear" or "Hi" needed)
If it's not your place of work, then the usual "Hi" or "Hello" will do.
The most common greeting I've seen for these types of email is the simple: