Improperly addressed email will result in email bouncing. Bouncing is when a mail message is returned to the sender. They will help you get your mail delivered properly. On the Internet some information is made available by what are called list servers or mailing lists. These are usually auto-mated processes that distribute information to a mailing list of users.
Individuals can subscribe to the list by sending mail to a given address.
This adds their name to the distribution list. Many times this is a valuable way of distributing important data to a small group of people. The White House has a mailing list to tell people of what the President has said in speeches. A good idea. Not so hot when many people from the same site begin subscribing to the same mailing list.