You will want to build a newsletter list for your customers so you can keep them in touch with the latest info on your company. You can use Yahoo groups for this but its not as professional as having one with your own companys idenfication behind it. Unless you are selling on Ebay or Amazon people tend to look at you with a little bit more legitamacy with your own newletter source. There are a few free ones out there but the one I like most is your mailing list provider which gives you up to 1000 email customers before you have to start paying. Its a good way to get started.