Answer: The concept of gender identity has eliminated the practice of writing Mr. Singh or Ms. Zheng. Below are your options.
1. If you know the person's given name and surname: Write Dear Suresh Singh or Dear Dawn Zheng. You can replace the formal Dear with the less formal Hello, Hi, Good day, or nothing, depending on your relationship with the reader.
2. If you know only the person's surname and job title: Write Director Singh or Vice-president Zheng, or whatever their title may be.
3. If you know only the person's given name and job title: Write Suresh or Dawn and drop the title.
4. If you do not know the person's name but know their job title: Write Director or Vice-president, or whatever their title may be.
5. If you do not know the person's name or job title: Find out. But if you can't, write Hello, Hi, Good day, Greetings, or whatever you think is acceptable to the reader.
As Nobel laureate Bob Dylan sang, "The times they are a-changing"; be a person of your time by changing with it.
