"Not In US Air Mail" Postal Marking?

Rate experts will chime in, but it appears that the 5c rate paid in Cuba was enough to move the cover by airmail from Santiago to a US arrival point, but not enough to move the cover by airmail within the US to Indiana, so the marking explains to the recipient why delivery took slower than possibly expected.

So, essentially, "For the domestic leg of the trip, your letter was not transported by airmail"?

I'm away from my rate literature but I agree with the explanation. The rate wasn't sufficient to include US domestic airmail.

This cover appears to have been intended by the recipient, Mr. Glick, to be flown on the inauguration of the Cuba's domestic internal airmail route 1 which happened on October 30 - 31, 1930. However, that service required postage of 10 centavos and this letter did not have enough postage to be flown on that flight. In addition to the lack of enough postage to go by air from Santiago de Cuba to Havana, Cuba, it also does not have the additional postage required for it to go by airmail on Foreign Air Mail Route Number 6 serviced by Pan Am, nor to go by air from Miami to New Harmony, Indiana. This cover also does not have the special rubber stamp cachet that was applied to covers flown on that Cuban inaugural internal flight service. Also, it is dated one day too early for the inaugural internal flight as the outbound flight from Havana to Santiago had the covers canceled on the 30th, while the return flight from Santiago back to Havana were canceled on the 31st. My guess is that without enough postage this letter would have gone on October 30, 1930 by ground from Santiago to Havana, by ship from Havana to Miami, then by rail and truck from Miami to New Harmony, Indiana.

That is correct to move by air in the U.S., but enough for ground service.

Another cover to sit alongside The Reverend Glick.

Kimo, fantastic answer! Thank you.

Hi Rod. Again with your cover to Mr. Glick "via Port-au-Prince" Haiti, the 5 centavo stamp would not have been enough to get the internal Cuban airmail on the inauguration of their internal air mail route 1, much less air mail service carried by Pan Am via Port-au-Prince and from there to Miami, and then from there to St. Joseph, Missouri. My guess is that Mr. Glick's hope to have it carried on that Cuban domestic inaugural flight and thence by air to Haiti, then Miami, and finally to St. Louis did not come to fruition due to his lack of knowing the air mail rates and supplying enough postage to make it happen. I notice that there is no rubber stamp cachet on this cover either - which it would have had if it had gone on the inaugural first first flight in Cuba. I would think that this went by traditional surface mail the entire distance.

Cheers Kimo,
not my cover, for sale on Delcampe.
Thanks for the explanation, one can only assume this was a regular occurrence?
The rubber stamp in existence would suggest this. perhaps the postal clerk at point of receival, failed to know the correct rates.

PS : why am I getting a spellcheck prompt with "receival" ?

Because it's primarily an Australianism, and web browsers are (intentionally?) poor at handling dialect words.

In most other dialects of English, one would say "receipt".

"Receival" is in the Chambers dictionary (a standard British dictionary) and is marked as "rare".

Yes. In The Century Dictionary, also. It is only in common usage in the Australian dialect.

Interesting.
I use it in everyday speech, I wasn't aware it was so unusual, elsewhere.
That's why I love the English Language....it's so.....pot-pourri.