We are working on a project that requires us to allow users to register to receive email notifications of certain events. There will potentially be tens or hundreds of thousands of email messages based on any one event.

I know that this is done every day all over the web, but what I don't know is how email campaigns are managed such that the sender is not blacklisted as a spammer when a single mail provider recognizes large numbers of messages from a single source -- I'm especially concerned with high profile mail providers like Yahoo, MSN, AOL, etc. who will likely receive the bulk of the messages that we send.

Is there a standard methodology that is employed in order to conduct legitimate email campaigns that users have voluntarily registered for?