It's a favourite saying among marketers and there is more than just an element of truth in it. In a web based business, if you can build up a list of interested contacts, then you can market to them and sell to them time and time again. That's what "the money is in the list" means and why it is so important to garner those contacts and to keep them warm.
To set about that, you need a mechanism that lets people sign up to your list. It's important to understand that people need to make this choice themselves. There are good reasons for that. In earlier Internet times, people often accepted emails from other people that they did not know as part of the fun and the excitement of a new medium. But then came the spammers who abused the system by sending millions of emails to sell products that most people did not want.
The spamming problem got so bad that the government was called on to intervene and declare spamming to be illegal. This doesn't mean that spamming has stopped. It's just that people know the situation and are that much more hostile when they receive unsolicited email. It's a natural human reaction. If you try to force someone to do something they don't want, then you will usually get a negative reaction like this on, instead of the positive one that you were hoping for.
The other problem is linked to the first. It goes like this. If you send an unsolicited email to another person, that person may take that as in intrusion on their liberty. They did not ask for your email and don't see why they should receive it. On the other hand, if you organize things so that people do ask to receive your information, the opposite is true. In that case people expect to hear from you and may even email you to ask why you haven't written!
So you need to use what is called a "double opt-in" system. It's a software application that is part of most autoresponder systems and it guarantees that the people who get added to your mailing list really do want to be on it.
You start by promoting your product or site on the web, via search engines, directories or advertising for example. People who are looking for related information will come across your site listed in the search engines or in the directories or they will click on your ad if it catches their eye.
Now they come through to your site that is where you can suggest that they sign up for your newsletter, for example. To do this you will have prepared a sign up form on the same page perhaps. The visitor fills in the form with their email address (otherwise they can't receive the newsletter) and other details such as their first name, any particular interest they have and so on.
It's probably best to keep the form simple at this stage. Getting into more detail can be done as and when they want to buy something, but don't scare them off at this stage. When they have filled in the form, it gets sent off from your site to the double opt-in application.
The double opt-in application then sends an email back to the person, explaining that you have received a request to sign up for the newsletter but need to check that it really was the same person who asked compared to the email address given. The idea is that it is not impossible that someone was playing a prank by giving an email address that was not their own.
The person then confirms that they really do want the newsletter, the double opt-in has done its job and you have added another willing contact to your list.
As your list grows in this way, you can use it to feed into an autoresponder that will send out emails at regular intervals and also give you feedback on the level of interest for each email. But this is why they say "the money is in the list" and how you can grow your business by carefully cultivating a community of enthusiastic clients.