This field determines what happens to email messages that have been identified by SpamAssassin as spam, based on their computed score and the recipient's spam threshold. The available options are :

Throw away
  Any messages classified as spam will be immediately deleted.
Deliver normally
  Spam will be delivered to the recipient's mailbox, but with X-Spam headers that can be used for filtering by a mail client.
Write to standard spam file ~/mail/spam
  Spam is written to the standard folder for manual analysis and deletion.
Write to mail file under home directory
  Spam is saved to the mail file under the user's home directory that you enter. To write to a Maildir format directory, put a / at the end of the filename.
Forward to email address
  Any messages classified as spam will be forwarded to the entered address.
Write to other file
  Spam will be written to the given mail file (or directory if the path ends with /), which can be anywhere on the server.