"Kindly"—as in: "We kindly request that you will send your subscription." There is nothing kind in your request and if there were, you would not so allude to it. "Kindly" in this case belongs to "send," as "We request that you will kindly send your subscription."
The word "kind" to describe a business letter—as "your kind favor"—is obviously misapplied. There is no element of "kindness" on either side of an ordinary business transaction.
The months are no longer alluded to as "inst.," "ult.," or "prox." [abbreviations of the Latin "instant" (present), "ultimo" (past), and "proximo" (next)] as "Yours of the 10th inst." Call the months by name, as "I have your letter of 10th May."
"Contents carefully noted" is superfluous and its impression on the reader is a blank.
"I enclose herewith." "Herewith" in this sense means in the envelope. This fact is already expressed in the word "enclose."
Avoid abbreviations of ordinary words in the body or the closing of a letter, as "Resp. Yrs." instead of "Respectfully yours."
The word "Company" should not be abbreviated unless the symbol "&" is used. But the safest plan in writing to a company is to write the name exactly as they write it themselves or as it appears on their letterheads.
