This one showed up, looking just like those presorted notices from one's health insurance, stating that the privacy policy has changed or whatever. But nope, it's money. The accompanying letter says it's a State and Federal Medical Loss Ratio Rebate. I googled that and don't understand entirely what it is, but it seems to be a rebate they'll send everyone because they charged too much based on what they paid out, or something.
This one also totally looked like junk mail. But was a check for a class action suit I had opted into. Apparently I got $127.14 for Uber sending me an unsolicited text message (probably when I signed up for something to get some Swagbucks). Sure, send me all the text messages you want, at those rates.
I also got a few others recently, from credit cards I had accounts with in years past, that also looked like those unsolicited offers of 30.00% APR loans or whatever, that I happened to open.
So, yeah, open your mail, even if it looks just like junk mail you receive from these companies all the time. I hope I haven't recycled any envelopes that contained checks.