Most often when I get an email or message from an international student, the first greeting is Dear Sir. As soon as they find out I am a woman, I sometimes am addressed as dear. This has happened to me at least three times which is three times too many.
In Canada a woman, especially one you do not know; is not addressed as dear. Please do not use the word dear.
So how do you address a woman?
When emailing or writing to a woman, address her as Ms. (Last Name) or Ms. (Full Name – First and Last). This is the most appropriate way to address someone of the opposite sex. When that person replies, they may indicate if they want to be addressed as Mrs. or Ms. If you know if the woman is married you may address her as Mrs. (Last Name). For example my name is Helen Khan but I should be addressed as either Ms. Khan or Mrs. Khan, both ways are appropriate but Ms. Khan is never not appropriate.
If you are meeting them face to face, in a formal setting such as an office, you will be advised by the receptionist or the individual how they want to be addressed. For example, the receptionist may say, Mrs. Khan will now see you. Or Mrs. Khan may say, “Hello, I’m Mrs. Khan (or Helen Khan), how may I help you?” You will lonely use the first name once you have permission to do so but you will never address them as dear; at least if you want to be respected.
The person you say dear to may continue to serve you and be polite (Canadians are extremely polite) but they will think poorly of you even while they are smiling at you. You do not want to be shamed in this manner.
If you are addressing a woman through email or a letter, again it is always polite to address someone formally as Ms. or Mrs. (Last name or First and Last name). As one, though, who is writing to the same sex, you have a little more leeway than your male counterpart and may start off with Dear Helen. Although this is an informal way of addressing someone, you will be forgiven, unless of course, you are applying for a job, then you must be formal and correct.
Dear Madam is also appropriate, although less seldom used.