How to address a woman in a letter?
When writing a letter or an e-mail to a man I know the (sur-)name of ("Smith"), I would write:
Dear Mr. Smith,
What should I use when addressing a woman?
Is it (like for married women):
Dear Mrs. Smith,
Dear Ms./Miss Smith,
What is more polite, particularly as I do not know whether she is married (coverture)?
The above is an amazing question regarding the usage of these shorthand forms. Now, I tell the asker to look all these words up in a dictionary, and I'mma do just that for you here as well:
used in front of the family name of a woman who is not married to address her politely, to write to her, or to talk about her
This entry in the Longman Dictionary of Contemporary English Online actually includes a useful usage note:
► Some unmarried women prefer to be addressed as Ms because it does not draw attention to whether or not they are married.
Wowie, this already answers the question, but let's go ahead and explore the dictionary further.
Mrs British English, Mrs. American English
So this dictionary includes this particular difference between British and American varieties of English. Perfect!
used before a married woman’s family name to be polite when you are speaking to her, writing to her, or talking about her
Again, this entry includes the following useful note:
► Some women prefer to be addressed as Ms because it does not draw attention to whether or not they are married.
This note would also answer the question.
Finally, let's look at the entry for Ms:
Ms British English, Ms. American English
used before a woman’s family name when she does not want to be called ‘Mrs’ or ‘Miss’, or when you do not know whether she is married or not
To conclude, obviously the dictionary is quite enough to answer this particular asker's question. However, my comment (the second one, for those of you who can see them) was deleted for some odd reason. What I also did was flag this question as answerable by a dictionary – but nope, this flag was declined. Why do you encourage people to ask these kinda questions in the first place?
By the way, you can find similar information about Ms, Mrs, etc. in other learner's dictionaries such as the OALD or the Cambridge one. I think I actually linked to a meta post linking to those dictionaries but... yeah. It's evidently not needed.
Exhibit B (this one isn't so bad, but it just shows how idiotic the whole thing is when you proscribe dictionaries):
Usage of “Staying online”
I know that it means a person is reachable over the Internet.
Can I say it while speaking about phone calls?
Thanks for staying online. (Thanks for not hanging up with me).
Here I comment saying staying online isn't an idiom and you should use multiple dictionaries to check the meaning of online.
Basically, my comment clarifies some of the asker's doubts. Namely, online is used with technologies related to the internet, not phones, and staying online, due to its literal use isn't extended to mean "stay available" or whatever the heck the asker thinks it means. This also suggests to the asker that they modify their question a little, perhaps so that the potential answer (i.e., to the question How else would I go about saying this?) wouldn't be just Nope.
So, why do you think a comment telling the asker to look up something isn't needed there, and further, why do you think mine were so damn bad you had to delete them? I'm really looking forward to your explanations.