Sew 18th Century wrote me the loveliest letter, and ever since I have been remiss in my epistolary duty. To better prepare myself, I took a look at a lovely little imprint at work, The Fashionable American Letter Writer: or, The Art of Polite Correspondence (Providence: Edward and J.W. Cory. 1833) which is thus far the earliest letter writing manual I have found in that collection. Below you will find some examples about servants, or for servants.

Letter XXV.—Recommending a Man Servant.
Sir—
The bearer has served me with integrity and fidelity these three years, but having a desire to settle in New-York, he left my house about a week ago, and by a letter received from him this day, I find you are willing to employ him on my recommendation., and it is with the greatest pleasure that I comply with his request. His behavior while with me was strictly honest, sober, and diligent, and I doubt not but it will be the same with you. I have sent this enclosed in one to himself, and if you employ him, I hope he will give satisfaction.
I am, sir, your humble servant,

Letter LXX.—From a young Woman just gone to service, to her mother in the country.
Dear Mother—
It is now a month that I have been at Mr Wilson’s. My master and mistress are both worthy people, and greatly respected by all their neighbors. At my first coming here I thought every thing strange, and wondered to see such multitudes of people in the streets; but what I suffer most from is, the remembrance of yours and my father’s kindness; but I begin to be more reconciled to my state, as I know you were not able to support me at home. I return you a thousand thanks for the kind advice you was so good as to give me at parting, and I shall endeavor to practice them as long as I live. Let me hear from you as often as you have an opportunity. With my duty to you and father, and kind love to all friends, I remain ever,
Your most dutiful daughter,

Letter LXXI.—The Mother’s Answer.
My Dear Child—
I am glad to hear that you reside in so worthy a family. You know that we should never have parted with you had it not been for your good. If you continue virtuous and obliging, all the family will love and esteem you. Keep yourself employed as much as you can, and be always ready to assist your fellow servants. Never speak ill of anybody; but when you hear a bad story, try to soften it as much as you can. I am in great hopes that all the family are kind to you, from the good character I have heard of them. If you have any time to spare from your business, I hope you will spend some part of it reading your Bible, and other religious books. I pray for you daily, and there is nothing I desire more than my dear child’s happiness. Your father desires his blessing, and your brothers and sisters their kind love to you. Heaven bless you, my dear child, and continue you to be a comfort to us all, and particularly to
Your affectionate mother,