Well, as you know (because I had told you before I started really doing anything with Qubbles that might raise flags) Quibbles' was built from the ground up as a character full of contradictions, and aspects that tried to force other RPers to second guess both Quibbles and themselves.
Some aspects were designed to straddle the border between high skill, and legit magic. Such things included him "talking" to animals. And his mailbox. (Among other things.)
The mailbox was actually one of the first things that I came up with when designing him. (I had the situation, 'Person 1: Why does he have a mailbox? Me: For mail, obviously.' worked out for a long time. Really liked how utterly ridiculous it was.)
I wanted other people to be constantly guessing from a number of possibilities while interacting with Quibbles. Is he just a crazy old man? Is he actually magical? Does he just have access to some advanced tech?
And the thing about RPing him that made him difficult to pull off... was that none of these things have answers. I didn't design him to be that simple, because I didn't come up with answers to the kinds of questions I wanted people to ask. Not out of laziness, but because I wanted to make others come to their own conclusions and make their own decisions on how to interact. And to an extent I think I was successful at that.
So, so get back to the topic of his mailbox... It's a mystery. It can be magic. It can be nonsensical. It can be just a mailbox full of random, miscellaneous items that Quibbles has no reasonable explanation for having on his person... Because the mailbox isn't the mailbox. The mailbox is Quibbles. I wanted something that was parallel with the direction I wanted to take Quibbles.
And I think I succeeded at doing so in a lot of ways. The character himself was based off an old forum joke. (Quibbles, God of the Mammoth Birds.)
I tried to constantly change up his behavior, but leave certain things consistent. Quibbles would have his brief moments of serenity. Or say particularly insightful things. Immediately followed up by him breaking into a song about ground hogs.
P.S. I put too much effort into this sort of thing.