Packages in Cat Mail Co. are not all created equal. Early on, you can toss most parcels wherever they fit and call it a day. That stops working fast. As you progress, packages arrive with specific storage requirements, and ignoring them means destroyed deliveries, failed shifts, and unhappy recipients. This guide breaks down every constraint type, how to spot each one before it's too late, and exactly where each parcel needs to go.
What are package constraints in Cat Mail Co.?
Package constraints are special storage rules attached to certain parcels. Each constraint tells you something about how that package must be handled, whether that means keeping it cold, protecting it from light, or making sure nothing heavy sits on top of it. The tricky part is that the game does not always label constraints outright. You often have to read the recipient's description carefully and pick up on keyword clues to figure out what you're dealing with before you commit to a shelf spot.
Shelf storage overview
There are seven constraint types in total. Some are straightforward, like Weight and Fragile, which affect physical placement on shelves. Others require you to route parcels into specific rooms that you unlock as you progress through the game. Getting familiar with all of them early saves a lot of headaches.
All package constraints and how to store them properly
The table below covers every constraint currently in the game, the recipient dialogue clues that signal each one, and the correct storage method.
| Constraint | Recipient Clue Keywords | Storage Rule |
|---|---|---|
| Weight | "not lightweight", "it's heavy", "help you because it's heavy" | Apply six weight stickers plus one special heavy sticker. Always place at the bottom of a shelf. |
| Fragile | "it's a fragile box", "be cautious" | Store on top of a shelf. Nothing can be placed on top of a Fragile package. |
| Cold | "kept it cold", "refrigerated", "ice creams", "special fish delivery", "catnip seeds" | Must go in the cooler room or the package takes damage at shift end. |
| Warm | "stay warm", "fire dragon scales", "didn't let it cool down" | Must go in the heated room or the package takes damage at shift end. |
| Dark | "photographic films", "dark environment", "midnight spores", "stay away from the light" | Must go in the dark room. Unlock by clearing the parcel pile in the cooler room. |
| Light | "bright environment", "bright room", "sunflowers", "a lot of light" | Must go in the Light Room. Unlock by clearing the parcel pile in the Heating Room. |
| Partner/Love/Heart | No dialogue clue; detected by placing under the lamp to reveal a glowing heart | Both paired packages must stay together. Separating them causes the light beams to disappear. |
Weight packages
Weight packages need two things: the correct sticker application (six weight stickers and one special heavy sticker) and bottom-shelf placement. The stickers alone are not enough. A heavy package placed on top of lighter ones will crush whatever is underneath, which counts as damage. When in doubt, always clear the bottom row first before sliding a Weight parcel in.
Fragile packages
Fragile packages are the opposite problem. They cannot survive anything placed on them, so the only safe spot is the top of a shelf. If you run out of top-shelf space, you need to reorganize before accepting more Fragile parcels. Stacking anything on a Fragile package, even briefly, will damage it.
Fragile parcels go on top
Temperature rooms
Four constraint types require dedicated rooms rather than shelf positioning. Cold and Warm packages are the first two you will encounter. Missing the cooler or heated room at shift end means the package takes damage, so do not leave temperature-sensitive parcels sitting in the main storage area.
The Dark and Light rooms come later. You unlock the dark room by clearing the parcel pile inside the cooler room, and the Light Room opens after you clear the parcel pile in the Heating Room. Both rooms are gated behind that cleanup task, so prioritize clearing those piles as soon as you can to avoid being caught without the right room when a Dark or Light package arrives.
How do you identify Partner packages?
Partner (also called Love or Heart) packages are the most unusual constraint because recipient dialogue does not flag them directly. The only way to detect them is to hold the package under the lamp. A glowing heart will appear on it, and you will notice a second package that connects to it via two light beams. Both packages in the pair must be stored together. If they get separated, the light beams vanish, which is your signal that something has gone wrong with the placement.
How to repair a damaged package
Mistakes happen. A package ends up in the wrong room, gets dropped in water, or gets a sticker missed. Once you unlock the repair table, you can fix damaged parcels by placing them on it and clicking the cardboard to the left of the table. The repair restores the package to full condition, wiping any damage it has taken.
The catch: you can only repair 3 packages per shift. That limit makes it worth treating repairs as a backup rather than a routine fix. Spending all three repair slots early in a shift because of sloppy placement can leave you stuck with a destroyed package later when you actually need the option.
For more tips on reading recipient descriptions and matching parcels to the right recipients, the Cat Mail Co. guides collection has everything you need to sharpen your sorting skills. Cat Mail Co. is one of the more satisfying indie games to master precisely because the systems build on each other this way, and getting the storage rules locked in early makes the later shifts considerably less stressful.
