nothing to send. Go to the evisa website and follow the instructions it will tell you where to ‘apply’ online based on where you live in the USA. It’s very easy.
Don’t think it has anything to with where your plane tickets leave from in a given country
2) isn’t true for the USA. You need to apply at either the embassy or one of the consulates based on where you live. You need to show proof of your address for example a drivers license. So if you live in New York for example you can’t apply at the consulate in Los Angeles even if you are in California for a trip.
Being outside the US while applying is a different matter