Emails are replacing regular mails from the post office. Not only because it is cheaper, since you do not need to buy a stamp, it’s also definitely faster. Emails can be sent in as fast as five seconds, depending on the server, anywhere in the world.

No doubt emails are being used to distribute news letters, promotional mails, and other stuff. How then would you be able to round up email addresses to send those marketing mails you have? Here is where an opt-in list comes in.

An opt-in list is a directory of email address you can send to those mails to. Though it seems to be easy to find email addresses, if you are talking thousands in numbers, it is going to be hard.