興味のあるメッセージを少量送信する見知らぬ人と、それをスパムとして送信する場合は非常に近いものです。合法的なものをフィルタリングしないように注意する必要があります。

The difference between a stranger sending you a message that you might be interested in at a very low volume level, no repetition, just sending it to very few people, and that being done as spam - those things get close enough that you want to be careful never to filter out something that's legitimate.