Dialing, routing, addressing, and signaling. Pen registers and trap-and-trace devices are devices that may be used to collect the non-content portions of a communication. As I've previously written, contents refers to "any information concerning the substance, purport, or meaning" of a communication. Therefore, non-content dialing, routing, addressing, and signaling information is necessarily such information that does not concern any such information about a communication. Simple enough, right?

Well, it seemed simple enough to Congress. They proceeded with the intention to call an "email address" a communications "facility," moving it into the definitions of pen registers and trap-and-trace devices. This involves a convoluted notion that one communicates from email address to email address, much as one communicates from phone to phone. Obviously, this is nonsense, but that hasn't stopped law enforcement from seizing upon this expansion.

However, let's assume for a minute that an email address actually is a communications facility unto itself, and that when we communicate via email, the endpoints are actually email addresses. If we focus solely on the real-time interception of non-content information of an email communication, what is "dialing, routing, addressing, and signaling" information, and what is "any content concerning the substance, purport, or meaning" of that communication? Remember, this is still a message in transit across the Internet.

Here's what we know. Before the email message can be sent, there is already going to be a TCP connection established between the sending computer and the receiving computer. Only after the TCP connection is established may the actual communication take place. When that message gets to the remote computer, that remote computer is going to have to receive it, most likely via the SMTP. In this day and age of heavy spam and other deviousness online, it is very likely that the message is going to have to be formatted somewhat well in order to be delivered.

In order for a message to be properly formatted for receipt by the remote computer, the sending computer will send SMTP commands, continuing to send others, followed by the actual content of the message being sent, in response to replies from the remote computer. The sending computer will give, at a minimum, its name, the email address that is sending the message, the email address that is the destination of the message, and finally, the message. If these steps aren't followed, the message will not be delivered.

But there's more. Once a message is delivered, for a communication to be complete, the message must be read. There are many things that may be carried in a message to allow it to be understood. Obviously, the body of the message allows it to be understood. But we're concerned, also, with any information that concerns the substance, purport, or meaning of the message.

In a telephone call, a great deal of substance, purport, or meaning may be derived from the voice of the communicator. In email, there is no such voice. However, the sending address certainly gives a message voice. The personalizable "From:" header my also lend such a voice. Bayesian spam filters assign scores to a message based on tokens in the headers, and these can also lend a voice, as can such headers as message priorities and the "Received:" headers, which allow a message to be traced and in many mail programs, is used to sort messages by date (and not the "Date:" header.)

In short, the proper use of SMTP commands, the email addresses and addressing, as well as received headers and the nature of the contents of the headers all lend substance, purport, and meaning to a message. However, under the most common interpretations of the current laws, all of those pieces of content may be readily obtained by law enforcement agents under the Pen Register Act.