Read this quote from zimmermann in the code book.

in the past, if the government wanted to violate the privacy of ordinary citizens, it had to expend a certain amount of effort to intercept and steam open and read paper mail, or listen to and possibly transcribe spoken telephone conversations. this is analogous to catching fish with a hook and a line, one fish at a time. fortunately for freedom and democracy, this kind of labor-intensive monitoring is not practical on a large scale. today, electronic mail is gradually replacing conventional paper mail, and is soon to be the norm for everyone, not the novelty it is today. unlike paper mail, e-mail messages are just too easy to intercept and scan for interesting keywords. this can be done easily, routinely, automatically, and undetectably on a grand scale. this is analogous to driftnet fishing—making a quantitative and qualitative orwellian difference to the health of democracy.

what is the purpose of the quote from zimmermann?

it explains how much faster e-mail travels than ordinary mail.
it shows how easily digital mail can be monitored by outsiders.
it states exactly how many people use e-mail instead of regular mail.
it proves that e-mail is better for the health of democracy than regular mail.