If you can’t determine someone’s gender by their name then simply address the letter to the individual or the individual themselves by their formal name without a title. I can’t tell you how many letters I’ve gotten addressed to Mr. Ngozi Obi and I feel like screaming at the top of my lungs, I’m a woman, I was born a woman and I love being a woman so please don’t address me as Mr. The next thing I get all the time are letters addressed to Mrs. Ngozi Obi or people walking up and calling me Mrs. Obi. To that I always feel like saying, I’m not married and especially not to my father. People need to take time to find out rather than assuming.
Personally, if you must address me with a title then Dr. Ngozi Obi is appropriate. Most people think it’s pretentious but I have a PharmD. so I’m not “stuck up” by having people call me Dr. Obi. If it’s too much for you to call me Dr. Obi then drop the title and call me Ngozi Obi but please don’t mispronounce my name by calling me “Nosy” the g is not silence. If that is still too much then Zi will do. Why Zi?, you ask. Z and I are the last two letters of my first name and it’s been my nickname since my mom started calling me that at two years of age!
I hope this helps a lot of people!