Yeah, SmartPost is kind of iffy, only because it uses the post office.
It doesn't surprise me that you didn't get much of what you sent yourself.
I commented how some government office mail came from downtown, which uses the same post office that is used by my neighborhood. the postmark shows it was sent out the same day or day after I was in contact with the office but it took 2 weeks to get to me, even though it was sent out at the same post office that delivers mail to my home.
I'm not sure how yours works, but when I lived in a single-office town, they wouldn't sort mail there. It all got gathered up, taken to a city about 30 miles away, sorted, and what was meant for the local office was sent back. Only then did it get put into carrier routes and readied for delivery.
You could usually depend on 4-5 days between the letter hitting the post office's mail slot and arriving at the end delivery point.
I live in Pittsburgh.
It was from a government office. I didn't even receive them until after the deadline they stated I needed to provide 2 additional forms to them
(post is archived)