The Unites States Postal Service has strict requirments on how international mail is addressed and has begun returning mail to the senders for non-compliance. There is a link on the Mail Service web page to a document on the regulations. A brief overview is listed below reflecting common issues that the Mail Service department and the Phillips Hall Post Office encounter.
The addressee’s full legal name and complete address must appear legibly with roman letters and Arabic numerals, all placed lengthwise on one side of the item. For parcels, addresses should also appear on a separate slip enclosed in the parcel.
All lines of the delivery address should appear in all capital letters. The city destination must appear in capital letters together with the correct post code number or delivery zone number, if any. The last line of the address must show only the country name, written in full (no abbreviations) and in capital letters. If possible, the address should have no more than five lines. For example:
MS CRISTINA CRUZ
APARTADO 3068
46807 PUERTO VALLARTA JALISCO
MEXICO
MR THOMAS CLARK
117 RUSSELL DRIVE
LONDON WIP 6HQ
GREAT BRITAIN
Exception: To Canada, there must be two spaces between the province abbreviation and the postal code, as shown below between “ON” and “K1A 0B1”:
MS HELEN SAUNDERS
1010 CLEAR STREET
OTTAWA ON K1A 0B1
CANADA
4. A complete return address must include the sender’s full legal name and complete return address in roman letters and Arabic numerals — it may not include just initials except where they are an adopted trade name.
https://www.ithaca.edu/intercom/article.php/20141106163359237