This section is from the book "Scientific American Reference Book. A Manual for the Office, Household and Shop", by Albert A. Hopkins, A. Russell Bond. Also available from Amazon: Scientific American Reference Book.
Mail matter should be addressed legibly and completely, giving the name of the postoffice. county and State, and the postoffice box of the person addressed, if he has one; if to a city having a free delivery, the street and number should be added. To secure return to the sender in case of misdirection or insufficient payment of postage, his name should be written or printed upon the upper left-hand corner of all mail matter; it will then be returned to the sender, if not called for at its destination, without going to the Dead Letter Office, and, if a letter, it will be returned free.
Dispatch is hastened by mailing early, especially when large numbers of letters, newspapers or circulars are mailed at once.
When a number of letters or circulars are mailed together, addressed to the same destination, it is well to tie them in bundles with the addresses facing the same side. On letters for places in foreign countries, especially Canada and England, in which many post-offices have the same name as offices in the United States, the name of the country as well as postoffice should be given in full. Letters addressed, for instance, merely to "London," without adding "England," are frequently sent to London, Canada, and vice versa, thereby causing delay, and often serious loss. Letters addressed to Burlington, N. S. (Nova Scotia), often go to Burlington, New York, on account of the resemblance between S and Y when carelessly written.
Thin envelopes, or those made of weak or poor, unsubstantial paper, should not be used, especially for large packages. Being often handled, and subjected to pressure and friction in the mail bags, such envelopes are frequently torn open or burst, without fault of those who handle them. It is best to use Stamped Envelopes wherever it is convenient and practicable to do so.
All valuable matter should be registered. Registry fee is eight cents, which, with full postage, must be prepaid, and name and address of sender must be given on the outside of envelope or wrapper. Money should be sent by a money order or registered letter; otherwise it is liable to be lost.
Patrons in cities where letter carriers are employed are advised to provide letter boxes at places or private residences, thereby saving much delay in the delivery of mail matter.
Postage stamps should be placed upon the upper right-hand corner of the address side of all the mail matter, care being taken that they are securely affixed.
A subscriber to a newspaper or periodical who changes his residence and postoffice should at once notify the publisher, and have the publication sent to his new address.
Publishers and news agents mailing second-class matter in quantities, will facilitate its distribution, and often hasten its dispatch, by separating such matter by States and Territories and the larger cities.
That is, matter addressed for delivery at hotels, should be returned to the postoffice as soon as it is evident that it will not be claimed. Proprietors of hotels, officers of clubs and boards of trade, or exchanges, should not hold unclaimed letters longer than ten days, except at the request of the person addressed, and should re-direct them for forwarding, if the present address is known; otherwise they should be returned to the postoffice.
Letters addressed to persons temporarily sojourning in a city where the Free Delivery System is in operation should be marked "Transient" or "General Delivery," if not addressed to a street and number or some other designated place of delivery. - Post Office Guide.