What is the interest for the destination country to know if the mail it distributes comes from its country or from foreign?
At the limit, it could facilitate the sorting of the sending country to know more quickly if the postcard remains in the country or if it must go internationally.
But the indication of the country is anyway already in the address.
Hello,
I tried to search for the relevant regulation but couldnât find it - would you kindly let me know where it is?
UPU Univeral Postal Union in Berne Switerland and âeveryâ post office regulations in most of the world, at least Canada, Europe, America. Has this information. Ask them? Itâs posted among the Universal Postal Rules. But all I was told is that not all post offices are fully manned or operaltional like we are here in the US. If you want to follow the rules, do. If you donât, donât. I pay too much in postage to want my mail delayed. For me itâs not an inconvenience to write PAR AVION AIRMAIL on an envelope and package, BTW the rules are for packages too. Good Luck! Postcards too! I just know from experience my mail moves faster when I do. âŚ
This is from the UPU âŚIt is important to note that the term âairmailâ in the Regulations does not necessarily refer to a mode of transport.
Rather, it can refer to a product. This is a common source of confusion. The UPU Regulations once referred to
airmail as priority mail. However, between countries in close proximity, it can be faster to use surface transport.
Many countries still call their fastest international letter or parcel mail product âairmailâ in dealing with their customers, even though some of it travels by surface.
In UPU standards, mail category is defined in code list 115, as follows:
â A â Airmail or priority mail
â B â S.A.L. mail/non-priority mail
â C â Surface mail/non-priority mail
â D â Priority mail sent by surface transportation (optional code)
rules rules rules and even more for customs. Sigh. This is only one of hundreds of things in regulations for PAR AVION AIRMAIL. Class is over. GOOD LUCK
USPS International Mail Manual section 244 still states to use Par Avion/Air Mail for First Class International (letters, cards, flats, packages) even though air is now the default method of transport.
Does it help? I stopped using the endorsement after the cessation of surface mail but then went back to using it since it couldnât hurt (and it looks nice). I have not noticed any difference in transit time.
USPS fully functional and operational? Whoever told you that doesnât get out much. I am both former career USPS and a lifelong customer. 
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