My mom was like this. It annoyed the shit out of me. It continued well into my twenties because I was moving a lot and always kept a permanent address at my parents’ house. It only stopped when I finally had complete independence; changed my permanent address, changed my mailing address everywhere, had my own car on my name, doing my own taxes etc. It still creates problems, though. Last year a tax form related to some old account was sent to my parents’ house. I only found out about it months after I’d filed my taxes and my mom was all “oops, this came in the mail for you and it got lost under a pile of crap on my desk”.
She failed to ever understand why this was a problem or why it bothered me. It’s bullshit, but I guess that’s how some parents are. They’ll never let you grow up, always treating you like a subordinate under their control. I handled it by yelling at her and being passive aggressive. The “sit her down and tell her how you feel” advice people like to give here just doesn’t translate well to real life annoying mother-fed up daughter situations. I have no advice except to say, don’t wait to move out officially like I did! As soon as you have any kind of address away from mom’s house get your mail forwarded there. It’s a pain in the ass to keep track when you’re moving and having mail forwarded, but it’s worth it.
start opening their mail
You can get a PO box and file a change of address.