Like most of you, I ship ammo UPS ground to other collectors in the US. If I don’t know them well, I ask for an ID showing they are 21 or over and a email or letter stating that they can legally own ammo (not a convicted felon, etc). Both are legal requirements and you can get in trouble with the Feds if you ship to minors or convicted felons.
I know that some States like Massachusetts have outlawed having ammo shipped in (only allowed to Massachusetts dealers), but didn’t have a list of the restrictions.
Just found the following in an ad on Gun Broker and think it is good advise. Sounds like this guy did his homework.
No sales to the following California Cities: Los Angeles , Oakland , Sacramento and San Francisco Sorry - No sales to AK, HI, MA, NYC, Montgomery County Maryland or Washington DC . Illinois buyers must provide a FOID in addition to a Driver’s License for ammo.