One mailing list can only go so far to serve the needs of pet owners since there are so many different types of pets and each category mailing list has different needs. Knowing this you may set up and offer several sub lists. You could have one for Dogs, Cats, Birds, Reptiles, etc. You can go even farther and split each of those list into several more specific lists. For dog owners you could have small dogs, large dogs, show dogs, etc, and do this for each pet category. Another example: You serve the Internet Marketing and home business market. You're teaching others how to build mailing list a profitable online businesses. Because you know that different businesses benefit from varied strategies, you can offer lists for the subgroups that you've identified. Affiliate and Network Marketing, Products Creation, self development, etc. You can build a more profitable online business by mailing list separating your targeted market into more specific mailing lists. You can also create a more unique relationship and deliver information that more specifically meets your clients individual needs.