This is such a good game! I love how satisfying everything feels, really smooth and well-made. :D
The only thing that could be improved, is maybe a bit more of a 'campaign' type gamemode, with a storyline, and challenges. Right now it only feels like there's a tutorial section, and an endless gamemode. A story/campaign mode would really improve this game.
Overall, a very well-made and clean game, a hidden gem amongst many other games.
(btw could you add something like a stamp eraser as an upgrade after you unlock the stamp? I accidentally got carried away stamping one of the parcels... it was unreadable after I was done :# )