I received an email from a forum inviting me to join. I watched that forum go from 10 members to over 200 in one day due to those emails.

I was wondering, is it SPAM if I sent out ONE email to a large list of people inviting them to my forum?

If not, how do I obtain targeted email lists? People who would actually WANT to know about my site.

I am VERY surprised that membership grew that much from sending out spam. Usually, doing so only irritates the receivers of the email. It's very possible that to make the new forum look active, the owner registered under mutliple usernames. Who knows.

spam is not the way forward. you will get yourself blacklisted.

It wouldn't be spam if you could partner with a site that is already established in your market. I've done that with email newsletters -- I find a site for writers, find out how much it costs to sponsor their newsletter, and then they mention my site when their next email blast goes out. Of course, the people they email have already opted in, which is why it's not spam.

-Tony