Tbh, as long as you make the mail obviously not placed by them they'll take it. (as in don't need to use a flag). Like they always shove (or drop) it into the

Tbh, as long as you make the mail obviously not placed by them they'll take it. (as in don't need to use a flag). Like they always shove (or drop) it into the mailbox so when there's letters that are obstructing the box from closing properly they know they didn't place them there so it's outgoing and they grab it.