Unlike postal mail or, later, the telephone, telegrams never received constitutional protection. Yet they were the quintessential nineteenth-century technology of communication, used extensively for business, government, and personal communication, much of which both senders and receivers would have wished to keep to themselves.
Why, then, did the courts not accept the analogies to postal mail offered by jurists like Thomas Cooley? Were not the privacy interests similar?
The underlying technology of the telegraph cut against secrecy. Rather like most electronic mail today, telegrams transited between sender and receiver with the aid of a third party who necessarily had access to the contents of the communication. This is, in essence, the “third-party problem,” and it continues to be a concern for courts when deciding on protections for email today.
This contrasts with postal mail, in which — except for postcards—carriers only know what today we would call “metadata”: the recipient or destination and, usually but not necessarily, the sender.
Additionally, and again similar to email today, many companies kept copies of messages they handled. Google does this so you can have access from any device; Western Union did it primarily to verify accuracy and honesty in transmission.
The presence of a third party in the process cut against arguments for maintaining the privacy of telegrams in the face of requests by others, particularly the government, for access. After all, if both sender and receiver had already voluntarily allowed telegraph operators to read their messages, what kind of secrecy could they reasonably expect?