I got one good answer in r/localmonero, but I thought I’d seek other opinions here.

I don’t want to use my own address. If I put some random fake “From” address and there’s a problem with the seller receiving the package, will USPS try to return it to that address and then I lose the cash? Just wondering what the rest of you guys are doing to remain anonymous when using cash by mail to buy monero.

3 anonymous shipping label services are listed below:

https://altcoinpostage.com/ https://cryptopostage.info/ https://cryptostamps.biz/

BTW, https://coinship.pro, which advertised itself on r/monero and is still listed on monerica.com, now seems to be defunct.