First off - go domestic if you're worried and problem is solved.
that being said, They can't open mail without a search warrant. If they have no way of proving that whatever is coming in from wherever your source is sending from is illegal they have no probable cause to execute a search or arrest.
If they want to try n nab you at the post office you will likely get a call saying that your package was delivered or held up there for some bs reason and to come pick it up. this would save them the wasted time of sitting waiting for when you might go pick up the package. They also will wait to do anything until you have officially taken possession of the package to make a move of any kind - in a controlled delivery they would wait for you to sign for and take the package at which point they can execute a search due to illegal materials being in your possession and in that property (your home)
domestic seems like it would definitely be the way to go for you. if for some reason you need to go international, here's a thought. you could also just strike up conversation with the post office employee behind the desk and mention how your relative just moved to moldova, greece, turkey, etc. and how they're always sending gifts or something to you to lessen suspicion as to the reason you're getting packs from overseas. all in all, minimize the risk you're taking and the suspicion you're raising and you'll most likely be safe
