And you want to do this in-house why? You should also take into account the audit recording of compliance with Anti-Spam laws - not an insignificant consideration. The fines can be large - even for an inadvertent slip-up. If you don't protect yourself and maintain credible records of IP's and timestamped opt-in recording etc. you can get into some fairly deep yogurt. This is why I and people not interested in hiring lawyers like to outsource this kind of thing to a company that has the legal and compliance issues covered + statistics reporting. Some companies do this and charge big buck but there are some reasonable players. E.g. aweber.com, getresponse etc.