"That's not good!"
Right from the beginning you had me hooked. There's a feeling of "playfulness" in your film, as if the figures would do these things given the chance. If I may elaborate-when a child plays with their toys you get sound effects, movement, and a really absurd story when different elements are squished together. Your film has captured that play-time atmosphere horribly well and you should be commended.
How many ways can a mailbox gobble up and dispatch citizens? You found many unique ways and even thought to include the flag in the ruckus. You have a creative script, funky animation style, and a wealth of voices to make this movie a very fun watch.
Some things I liked in detail:
-Your sound effect was hilarious for the rocket launcher.
-The stairs the postman climbs in the beginning-good timing. We know he's used to this particular mailbox because he has them handy.
-How "BOO" remains in the title. Clever.
-The fuzzy screen when the mailbox growls.
Others have already pointed out areas that need improvement- light flickers and misspelled words on the bottom of the screen- so I won't harp on those again. I did find that when I animate during the day I put thick blankets over the windows so the sunshine doesn't impede my progress. I don't know if that was your problem but I thought I'd throw it out there. You could always play the movie on an old projector (with FREE light flicker) and the complaints would go away.
Thank you for a wonderful film. I hope to see more in the future but take your time and churn out only good ones like MAILBOX OF DOOM!