Deflexion.com

Four years ago when I created the Reverse Spam Filtering page, I was using two spam mailboxes, which I called yellow and red. After a lot of experiments, I've decided that the best strategy, especially given the current state of IMAP clients¹, is to minimize the number of IMAP mailboxes that I use. I now use a single spam mailbox, which I call MaybeSpam². As I mentioned last week in IMAP Tip: Use a backup-all mailbox, I use server-side filters to sort my incoming email into mailboxes like these:

• list1
• list2
• listN
• green
• MaybeSpam

To make it easy to quickly visually scan my MaybeSpam mailbox and see if it contains any non-spam message (i.e., any false positive), I have set up my system so that:

1. Any non-list message with a score of 2 or more is delivered to the MaybeSpam box.
   
2. If a message has a score of 4 or more, inject the spam score into the beginning of the message's Subject.
3. If a message has a score of 7 or more, flag it with the IMAP \Deleted flag.
4. Set up my IMAP clients so that whenever the MaybeSpam mailbox is opened, it is automatically sorted by Subject, the focus is on the first message (the message with the lowest spam score), and messages with the \Deleted flag are not hidden.
   
5. For any non-spam message in the MaybeSpam box, remove the \Deleted flag if necessary, greenlist the sender, and move it to my green mailbox.
   
6. Delete and expunge the rest of the messages in the MaybeSpam box.
   

Here is the part of my Sieve script³ that does #1 and #3:

if header :contains "X-Spam-Level" "SSSSSSS"  {
addflag ["\\Deleted"];
fileinto "MaybeSpam";
stop;
}

if header :contains "X-Spam-Level" "SS" {
fileinto "MaybeSpam";
stop;
} 

#2, injecting the spam score into the beginning of the Subject, is done by SpamAssassin and how to configure this depends on your IMAP service provider. Most good IMAP providers, for example Tuffmail and FastMail.FM, let each user specify if and when the spam score should be injected into a message's Subject header line. I discuss this in the sort-by-score item in my list of What to Look For in an IMAP Service Provider.


¹ If all IMAP clients supported virtual mailboxes (aka saved searches or faceted mailboxes) and user-defined flags (aka IMAP keywords), I would probably have designed my system differently.

² I recommend that you call this mailbox 'MaybeSpam' rather than 'Spam' to make it clear that 1) this is a mailbox that needs to be periodically checked for non-spam messages, and 2) this is not a mailbox that is used to train your system's filters.

³ Instructions for how to do this with Procmail are in the Using SpamAssassin section of my Procmail Quick Start.

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