Think of something written down that nothing happens because of. The words are still there — you can read them, you can point at them — but they reach nobody and they move nobody. A rule on the wall that no one checks; an envelope in a tray that no one will ever open. Still there, and dead where it counts.
From the picture
寄不到也退不回的信
同一個畫面落在一封實體的信上：地址錯了所以送不到，背面沒寫寄件地址所以也退不回，於是它哪裡都去不了。這是理解上的連結，不是在說兩個意思誰從誰來。
noun · C1
A letter that the post office cannot deliver and cannot send back, because the address does not work and there is no way to find the person who sent it.
死信（無法投遞的信）
noun · C1
A law, rule, agreement or idea that is still officially there, but that people no longer obey or act on, so it has no real force any more.
名存實亡的規定