Here on DUG we do not accept any form of SPAM. That in our terms also means anything which is more marketing/link collections, than helpful member posts are also considered spam. Of course off-topic posts are also accepted, if the goal is to tightening the community members relationships. Like posting a Friday afternoon joke is ok.
Our website both have a number of spam detection functions which controls all posts here on DUG. That picks up most of the spam, by looking at a number of factors, like number of link in a post, but especially the members past posting history. A post from a newly registered member with no previous posts is more likely to be tracked as spam/abuse than a member with a long history of non-abusive posts.
But the automated function does not catch everything. Any member can also help us.
Click on the More button on almost any content in the system. When you report a post as abusive, then our moderators and admins are notified and can take action by either approving the post or deny it.
When a post has been denied, either by the system or by users and moderators, then the member who posted the content will get a notification. The notification comes with an option for the member to appeal the denial and explain if and why they think that their posts are not abusive/spam.
Members and posts which are deemed 100% (like some linking to spammy/illegal sites) are denied and removed without appeal rights.