Spamming thousands of people can be detected without knowing the content. And if you accept messages from other people than those you are following, you have to

Spamming thousands of people can be detected without knowing the content. And if you accept messages from other people than those you are following, you have to accept you will inevitably get some spam. It's like getting PGP encrypted email - you can't expect server spam filter to catch it based on its content and if you report it as a spam, server spam filter doesn't see the content.