Any of the three email marketing options offered by LexiConn can be setup to automatically add customers to your mailing list when they checkout from ShopSite (ShopSite Pro required). Information on each of the three email marketing options can be found at:
If you sign up for LexiConn's email marketing service, you will need to login to the mailing list application (http://lists.serverhost.net/) and set up list (either an empty list or one you have already used to import users). Once you have a list set up, send us an email at email@example.com and let us know the name of the list you would like to integrate with ShopSite.
ez-Newsletter and ConstantContact can also be set up to integrate your ShopSite with their mailing list. Contact them for details and they will assist you in setting it up.