The Mailman's locked container is one of the first obstacles you will come across in Dead Island 2. It requires Mailman's key to open, which, sadly, you won't be able to acquire on your first visit to the Bel-Air district.
You can get the Mailman's key by completing the Lost & Found quest, "My Mailman Was a Zombie!" in Dead Island 2. If you didn't know, Lost & Found quests are treasure hunt-style missions that reward some of the best loot in the game. They aren't exactly easy to complete, which is why we are here to explain how to complete this Lost & Found quest and get Mailman's key in Dead Island 2.
Where to find the Mailman's key in Dead Island 2
To start, "My Mailman Was a Zombie!" Lost & Found quest in Dead Island 2, you must progress through the main story, reach Venice Beach, and unlock fast travel. Once you do so, come back to Bel-Air, and look for the Mailman's truck. You can find the location of the truck in the screenshot above, whereas you can find the location of all three packages in the screenshot below.
When you return to the Mailman's Truck, you will find a document that requires a signature sitting beside it. Pick up the document to start the Lost & Found quest. Now, to get the Mailman's key, you have to locate and investigate three packages. You will find the key at the location of the third package.
The first package is in the Goat Pen house, which you also visit to collect evidence for Obi's keys in The Clean and Snatch Lost & Found quest. You can find it around the staircase near the front door of the house.
The second package is in Colt Swanson's mansion. You can find the package next to the big black fences near the entrance. The third and final package is near the garage of the house right of Curtis Sinclair's mansion, which you might have visited during the side quest," The Death of the Party."
Instead of the package, you will find a Slobber zombie called Wayne, The Mailman (yes, that mailman!), who you must defeat to get the Mailman keys.
Scurry back to the location of the mail van and open up the container to get a Rare-tier long-scope rifle called Raven.