Anyone on this thread who claims to address people in this way should learn some manners and appropriate writing skills.
For an older generation, not addressing people in this way this could definitely be considered bad manners.
And someone with the writing skills of Tolstoy might still follow this traditional form - but I understand what you mean.
So the only solution is to try to think what the recipient might prefer.
For myself, if a letter is not formal, I like my own first name with no Ms, Mrs, Miss.
I am not so keen on the halfway house of Mrs KindDogs H's surname. i.e
Mrs Jane Smith (the old style divorcee form) or Ms KindDogs
If I were to start again I would either keep my maiden name, or use it to make a double barrelled name with my husband's surname.
To some men of an old generation it would not be Mr John Smith either, but John Smith Esq.
So it was always unfair that a woman could not be Sarah MaidenName Esq f. version.