I'm talking about the "Dear so and so" line on a formal letter or email, and I'm wondering if they should still contain Ms. Mr, Mrs, etc.

As an example I'm doing interviews now and it's interesting to see how people address their letters when you basically have to guess if I'm a man or woman having never met me before. For one person, they listed on their resume they were a "brother" in a fraternity. They had a gender neutral name so we all assumed a man and addressed in emails as "Mr." turns out it was a coed fraternity and the applicant was a woman. We apologized but it got me wondering should we just forgo the practice? Is it better to just use the person's full name?