This is another excellent source. A prominent link on Dr. Grohol's page is to the suicide helpline mailing lists. It is a massive horizontal interactive encyclopedia. It is magic. It is also extremely public .
People often associate it with telephone technology, since that's how they connect via modem.
A better analogy is the post office. Information travels in addressed digital envelopes to and from its destination. It may pass through several computers along the way, each one passing it on to one closer to its destination. At each computer is an opportunity for information to be intercepted. This is why it is not considered wise to send credit card information by email or non-secure web form.