Folded, Spindled and Mutilated

Folded, Spindled and Mutilated.what does this mean?and examples?thank you very much!

When something larger than a standard letter was sent through the mail that could be damaged by various ways of cramming it into a small mailbox, it was often marked to ensure special handling with a stamp that said "Do not fold, spindle or mutilate". If you sent a large envelope that just contained a letter it would be fine if the postman folded it into the mail box, but if it was a photograph it would be ruined by the crease.