Spanish word 'auto cerrado'

What is an "auto cerrado" in the context of a letter or message, in a document written long before 'auto' was short for 'car'?
My guess is an envelope, but Im not sure...

Just a guess, but could it refer to a self-sealing envelope?

Sorry, my reply at #1 was dumb. Self-sealing envelopes certainly weren't around "long before 'auto' was short for 'car'."

Can you give an example in a complete sentence?

My GUESS is "auto close" ie when this is finished downloading, it will close by itself. Just a guess. "Self- closing?"; "these doors will close automatically?"

Before it had four wheels 'auto' used to mean verdict or court case and things like that. Wouls that make sense in the context?

It's not even a word not a proper expression. Just something that some company has made up for their own purposes.

Oops, I meant 'nor' a proper / correct expression....

I was thinking along the same lines as #5, but without the context we're all just guessing.

I reckon NorthAmerican is right.

auto referred to a court case or a verdict, as in 'auto de fé' an act of the inquisition.