Address them with, "Dear [full name]"/"Hello [full name]".
Address them by their given name (assuming you can tell which name is which).
Don't address them at all and use "Hello" / "Good morning/afternoon/evening" as your reply opener.
Don't address them or greet them at all; just launch into the main text of your reply.
Address them as Dr./Rev. whether they're a doctor/reverend or not.
Use a non-profession-related gender-neutral honorific such as Citizen, Comrade, Mx, Ser, etc
You always use gender-neutral honorifics so this would not be an issue for you.
You don't ever use honorifics at work for any reason so this would not be an issue for you.