Ah, good thinking on the caulk. I guess it’s slightly messy if you need to open it, but that’s easily dealt with. I guess you could even use wax… it’s better than nothing.
I actually use it mainly as a temperature sensor as far as how it’s set up in the SmartThings app for me (along with 12 other temp sensors), and the mail delivery only appears as a notification I set up through a custom SHM rule. That’s all I want - a ding when I get mail. Plus to keep all my ding notifications straight I paired this one with a TTS with Tasker. I used a fem Italian voice so when she says “MB” it sounds like “emma bee”, laugh.