Can I apply for a Type O-A visa by mail from Thailand to a Thai embassy in the US?

There IS a way it can be done (although I am NOT advocating it only explaining it).

The rule is you CANNOT apply for a visa to thailand from a thai consulate in another country while you're IN thailand.

I know people who get Non-O-A visas from the US every other year by:

flying to cambodia or the philippines, sending their passport (and the application, copies etc) to someone in the USA, having them post it to the consulate with a return addressed envelope to their house. Once they get the passport back with the visa in it they DHL or FedEx the passport to the person in what ever country they are in and THEN you can enter thailand on that new visa.

There is NO rule that says you have to be IN the country where you get the visa for thailand, ONLY that you can't be IN thailand and get a visa from a consulate in another country.

My US address is my sister’s house. She has forwarded documents sent to me at that address. If you have a similar arrangement in the US then you could try mailing “from within the US” that way. It will cost a bit more and everything will take longer in the mail.

I thought we had covered how you get a year extension by getting a 90 day single entry Non-O visa <- (note there is NO A after the O) either inside the country at the thai immigration office OR from a thai consulate in a nearby country. THEN when you have 30 days or less left on that visa you apply for a yearly extension of stay at your immigration office by meeting the financial requirements.

I thought you were going to check with your immigration office in Udon as far as if you could get the 90 day Non-O visa from them. What did they say?

You CANNOT apply for a Non-O-A visa OR ANY visa (other than the thai elite visa) from INSIDE of thailand.