不好意思，我英文不好sorry,my English is bad,l try to help you. I’m children Chinese teacher Some times we say Dear person name,But that means this people is really your friends,like boy/girl friend亲爱的朋友名字，or it’s your family people,like mom/dad.亲爱的爸爸/妈妈 So we allays used for someone’s name 致某人的名字

If you are writing an email, you can use 尊敬的X先生/女士for someone you know but not familiar with, use 敬爱的X老师/教授for your teacher or professor, use XX(given name) for your friends.

我们很少用 亲爱的***作为开场，正式一点是 用 尊敬的**先生/女士，您好！

In formal situation,you can say"尊敬的...先生/女士”。