Mass unsolicited emails are referred to as spam or junk email. The Zimbra Collaboration Suite installs the SpamAssassin anti-spam software as the mail filter to identify spam mail. When you installed the Zimbra Collaboration Suite, the anti-spam software is automatically enabled.
You can enable or disable this protection and set rules for handling spam from the Global Settings>Anti-Spam tab. How these rules are configured determine how aggressively spam is filtered. The following options can be changed:
Kill percent at 75%. Mail that is scored at 75% is considered spam and is not delivered.
Tag percent at 33%. Mail that is scored at 33% is considered spam and is delivered to the Junk folder.
Subject prefix field is blank. The prefix entered in this field is added to the subject line for messages tagged as spam.
When ZCS was installed, an automated spam training filter was enabled. Two mail accounts were created.
The Spam Training User address receives mail notification about mail that was not marked as junk, but should have been.
The Non-Spam (HAM) Training User address receives mail notification about mail that was marked as junk but should not have been.
When a message is tagged as spam, the message is delivered to the recipient’s Junk folder. Users can view the number of unread messages and can open the Junk folder to review the messages marked as spam.
To turn on or off RBL's refer to the Administrator Guide, Managing the Zimbra Collaboration Suite chapter.