Friends Challenge-Response System
The Friends Challenge-Response System or "Friends" is a spam prevention system that will check incoming mail based upon a list of known email addresses. The Friends system can operate in the following modes:
In this mode if a message is received from an unknown sender, an email is sent to this person requesting them to respond to confirm that they are human. If a response is received, the original message will be delivered; else it remains in the Spam folder. On a regular basis a status report message can be sent to the user providing information of the Friends system and any mail pending delivery.
This is the highest level of safety. Mail is only allowed through if the sender is in the list of known friends. If this is not the case, the inbound message is bounced with a configurable notification that this person is not accepting mail from unknown senders.
This mode keeps track of Friends but does not block anything or request confirmation. It is similar to "Confirm mode" except it does not hold messages from unknown senders, and it does not send a message to them requesting confirmation. So it simply applies the friends list, accepting mail from known friends and leaving unknown ones for another feature/filter rule to deal with.
In this mode if a message is received from an unknown sender and only if it has a SmiteSpam rating more than indicated, the message is blocked. However, unlike in 'Confirm mode', a request confirmation message is never sent.
In this mode if a message is received from an unknown sender and only if it has a SmiteSpam rating more than indicated, the message is blocked and a request confirmation message is sent out similar to 'Confirm mode'.
Using either Silent or SmiteSpam mode is recommended, as this will block suspected spam by placing it in your Spam folder, while allowing you to configure the level of spam to block. The default level is 10, but if this is blocking too much real mail, it can be increased. In addition, SmiteSpam mode will send a challenge email to the sender giving them a chance to be added to your Friends allow list. Once in this list, mail from that sender will not be blocked again. By default, anyone you mail first gets added to the allow list automatically.
Blocked mail can be read in the Spam folder, and this is even accessible through IMAP. If you ever see real mail in the Spam folder and want to prevent it from happening again, just log into webmail to tag it as "not spam" or "accept sender". This automatically moves the mail to the Inbox and puts the sender in your Friends allow list.
The Friends system may be temporarily disabled if an urgent message is expected from an unknown address using the "Disable Blocking" button. This will effectively turn off any email blocking by the Friends system for a period of three hours.
The following settings can be set by the user:
The message sent to users to request confirmation that they are human.
A set of rules defining email that is exempt from the friends email filtering system.
A list of pending messages currently awaiting confirmation that the sender is human.
List of messages received and sent.
Log of actions performed on the Friends system.