US Stampless Folded Letter 1810/1811 - Fascinating!

The Flash was a cargo ship for carry packages they have a name for those ship I don't remember it and google on an iPhone is a pain

Thanks for you thoughts Kimo. But I wasn't suggesting that the Swedish ambassador to Switzerland carried the letter. My premise on this is that since her late husband (he died in 1802) was the Swedish ambassador to France, the Madame de Sael may have still had connections in the Swedish court, through whom she, or rather her son Auguste, who wrote the letter, could have asked to carry the letter. I came to that possibility because of Norfolk's proximity to the capital in Washington. If it was just a friend, why not look for a friend travelling to New York itself?
As I said it's only a theory. And you are correct, it could have been anyone they trusted. But it wasn't the writer himself because he does mention in the letter that he had hoped to come to the US - he did seem very familiar with the gentlemen he was writing to - but couldn't so that is why he was sending the letter. If he had come himself, he would have happily shown up at their offices in New York.
And agreed, the lack of markings supports all sorts of theories. Many of which I've considered. That's why, at this point, almost anything is possible.

Norfolk is 200 miles from Washington by modern highways and I would imagine the distance would have been even greater in the early 1800s when there were few roads. By water it is even further. Virginia is a very large state and Norfolk near the southern border, a few miles from the North Carolina border.

Given that her husband had died in 1802 which would have been 8 or 9 years before this letter was sent, and given the unlikeliness of such a personal and non-official letter I would think it even less likely that it could have gone by diplomatic pouch. When trying to find a solution to a mystery it is always best to start with the most likely and disprove that before getting into unlikely answers. Being carried by a friend who happened to be going to the US in their baggage and then being mailed when that friend arrived at their destination in the US is the most likely answer. I have done this myself for friends when I was in countries with marginal postal services and was headed back to the US. Sometimes I would wind up with dozens of letters from a number of American citizens who were living in such other countries including everything from personal letters to bill payment letters.

Ok, I'll admit I was wrong on the distance. For some reason I thought it was closer. Apologies to all.
However, and I'm not saying the diplomatic route is the ultimate answer to this, but I'm only suggesting that her family ties, in many countries on the continent, to government officials, may be an answer. A friend travelling there is also a very real possibility. I will never know the real story.

My only point on the diplomatic pouch being a stretch is that such mail needs to be marked as such, usually by hand. I know as I was in the diplomatic service myself for over 30 years and know all of the very strict rules about using the pouch and how they are based on the agreement between two countries that establish and permit diplomatic relations between those countries. Mail in the pouch is considered to be privileged official mail under the diplomatic agreement between the countries. Bending or breaking those rules would put the mutual diplomatic agreement between those countries at risk. Also, "has been" ambassadors and the like are not given much deference especially by a current ambassador as doing so would be seen by most current ambassadors as undermining their position as THE ambassador. Anything is possible, but going by diplomatic pouch of a third country is perhaps one of the least likely of all of the possible explanations.

area66 - It is only now that I am returning to this thread having stopped following it as there were no more posts last December and in the first half of this month.

Now that I am reading your post of 01/16/2016 I cannot believe my eyes for it was myself who had made those two silly mistakes (and repeated heterographs on top of everything!) that are so difficult for me to explain because the script in that place was perfectly clear to read.

Your explanation is perfectly reasonable but considering my age I might actually be returning to my early stages of learning French some 60 years ago when I had learned this language in a self-taught crash course of 60 lessons (at the rate of one lesson a day) during the two months of my summer holiday while working on my parents' farm.

Thank you very much for pointing them out. Any corrections of my mistakes are always welcome.

Cheers,

Florián