Here’s what happened when I shut down comments on posts older than a few days:
Apparently the spammers’ scripts can’t keep up with a short window and most comments happen in a few days, so this seems like a workable compromise. I know for a fact that spammers also employ humans to type comments, but that model doesn’t scale well at all.
Akismet disposes of most spam automatically, but presents me with a list of comments that it can’t classify. That list amounts to 10% of the daily catch, meaning I had to process that much junk every day just to keep up. I don’t know why Akismet can’t classify total gibberish as obvious spam and automatically delete it, but that’s how Akismet works.
As mentioned in the sidebar, send me a note to comment on an older post.
Now you know …