Email marketing has changed through the years. Back in the late 90's when I came online we worked with something called Major Domo. This was the beginning of mailing list management. You would have this set up on your own domain and send emails to everyone who belonged to your 'list'. To subscribe people didn't fill out a form, they had to send a message to the Major Domo on your server and say, "Subscribe".
To unsubscribe, do the same thing email list but with "Unsubscribe". Major Domo in Latin means "Head Of The House" and this is what you became when you sent out an email to the people who were on your house list. Unix/Perl based list management is how we built our first house list with our kitchenware business. We later created a second list with our online vitamin stores.
Then we had a fast growing list with people who were on our Bread Making Forums and subscribed to receive not only updates on the forums but also weekly and sometimes daily recipes that we sent out. Groups grew beyond Major Domo into the popular Yahoo List Groups and then Bulletin Board systems. This is when moderation and exclusively really began to stick. If you were 'admitted' or 'approved' to a list you were given strict guidelines to follow and in turn for adhering to these guidelines you were given access to regular email updates, member interactions and 'insider' information.