[jamesknelson]

Actually... they have built such a system! It’s long gone now, but some major cities used to have a mail delivery system built on underground pneumatic tubes.

https://en.m.wikipedia.org/wiki/Pneumatic_tube_mail_in_New_Y...

[Filligree]

Do you know what killed it?

[metaphor]

Discussed in the wiki: https://en.m.wikipedia.org/wiki/Pneumatic_tube_mail_in_New_Y...

[gregschlom]

The electricity-based message transmission systems (telegrams, fax, email, etc)