ListServe Pro, or LSP was written in order to provide webmasters with an alternate solution to server-based "List-Serve" (Newsletter) facilities. Such services offer website authors the ability to collect and manage email addresses of people who want to hear about updates and news regarding the sites they're interested in - running a ListServe allows webmasters to build community and communicate with those who are interested in their pages. The drawback with those systems, however, is that they typically rely on cgi-bin functions which most ISP's are reluctant to give their users access to as they pose a security risk owing to nature of server-based software. LSP will provide your website with ListServe functionality - all you need is an SMTP and POP3 account (these are typical offerings from any ISP)!
NOTE that LSP is not for use as Spamming Software! Any user who is caught or reported to be using ListServe Pro in a spamming capacity will have their usage license revoked and may be pursued for damages incurred in a court of law. Your usage of the ListServe Pro softwar eimplies that you understand this limitation and agree to it!