The spam handling programs in the SpamCorral package work with mail messages that, instead of being delivered, were placed in a directory (called the spam corral) by a mail filter of some kind. What they expect to find in that directory is a collection of ready-for-delivery messages that simply got sidelined because they contain spam.
Upon receipt of a reply to a spam notification, the spam release program expects to be able to take the ready-for-delivery message and remail it to the recipient. It also expects that this remail operation be carried out without the remailed message being scanned for spam a second time around.
The virus/spam filter, in the package MailCorral, works hand in glove with SpamCorral by: 1) placing spam into the spam corral in the proper, ready-for-delivery format and adding a special header giving spam statistics that SpamCorral passes on to the recipient to indicate why the message is considered spam; 2) tagging each piece of spam with a secret key that will allow it to pass through the filter a second time, untouched, thereby allowing SpamCorral to remail released spam.
Although it should be possible to easily change the programs in the SpamCorral package to work with other mail filters, SpamCorral was specifically designed to work with MailCorral so the interopertion between the two is seamless.