I think the identity thing is overplayed. I still address Dear Sir/Madam, although I hate formalities. I'll leave the next generation to new thinking. I think I'll be long gone before anyone starts to seriously get pulled up on it.
The deteriation of the standards of English, I am no expert I hasten to add, always bugs me. Why not address people as "Dear Sir/Madam" it is only polite. When I worked, the company style demanded that I use my first name in communications with customers. Some would pick that and call me by my first name. I always bristled at that.......but then, I am just old fashioned. ..
"Dear Sir" if you are writing to someone who's been knighted
"Dear sir" to a random bloke you've never met
"Dear sir / madam" if you have no idea who will be reading it
"Greetings" or "Howdy" if you want to be a bit less formal than "Hi", "Hey" or "Hello"
For work teams of multi gender, I've used the "Folks" salutation occasionally.
Good morning [or afternoon] assumes the message will be read shortly after sending - this is a gross presumption ...