Why isn't autolearning working for me? (aka: "autolearn=no")

Lots of people seem to be confused by the "autolearn=no" statement in the default X-Spam-Status header. There are usually questions regarding whether or not "no" means SpamAssassin is not autolearning at all. What it actually means is that the specific message which includes the "autolearn=no" part was not autolearned, not that autolearning is disabled or somehow broken.

The three values that can be displayed are "no" (autolearning did not occur), "ham" (the message was learned as ham), and "spam" (the message was learned as spam).

For more information, please read the Mail::SpamAssassin::Conf documentation.