When I saw a post on this site which can be considered spam, I usually flagged as spam and also downvoted it. I thought that this was the right thing to do - IIRC the downvotes decrease the visibility of a post in some views of the site.
Today I saw the following comment:
Tangential but important: spam posts should be neither downvoted nor closed. They should be flagged as spam. Each flag carries an automatic downvote, and six flags delete the post and deal a penalty to the author (-100 rep, and speedy progress toward IP-based ban). The guidance from SE is that nothing else should be done to spam posts, so that the signal that goes to automatic spam fighting system is as clear as possible. [Other kinds of activity raise suspicion that it's some unpopular post on which spam flags were used improperly.]
Could someone confirm what is the official policy for dealing with spam? (Ideally with a link to meta.SE, if the official policy is formulated somewhere on that site.)
I suppose that I am not the only user not knowing that spam posts should not be downvoted, so I think that making a post about this on meta could make more users aware of this.