Only between friends. And you had to actually give a child permission and your signature as a parent via the 3DS to let a child receive Swapnote stuff. I was a responsible parent.
If Nintendo was a person, I would punch them in the face. Goddammit. I used Swapnote to "text" my daughter and ask her how her school day went. Now I can't even do this anymore.
That's not true. You could activate street pass on swapnote and send mails with pictures to other swap note users who also activated street pass. I sent pictures of a pussy for a while. (It was just a cat.)