|photo by HowardLake|
Any of the reputable bulk email service providers (ESPs) will expect you to have received permission to email your subscribers. In many cases, this requirement can be satisfied by having a public sign-up form. Of course, this isn't an option for organizations sending private messages to a membership list.
Just because someone has agreed to become a member, paying or free, doesn't mean you have permission to email them - unless you have asked for it during the membership process.
Granted, this may seem like overkill. Generally, when someone becomes a member, they'll expect to receive some email communication. But the problem likely won't arise from your members. It'll come when you (wisely) decide to use a bulk ESP to communicate with them. That is when it will be important to be able to demonstrate that you have permission. While you might be asked to provide proof of permission for all subscribers, being able to show a process that gathers this permission will often satisfy the requirement.
Any organization that wants to communicate with its members in a way that is compliant in this increasingly regulated industry should include a simple request for permission during their membership process. This will save you time and trouble in the future.