Question

How does FogBugz decide how to sort emails and block spam?

Answer 1

If you're asking yourself  "Why does this thing say 'still training' when I've been using it for weeks?" then read on! Or even if you're not asking yourself this question, yet want to know how FogBugz learns to zap your spam, read on.  

In a Nutshell:
FogBugz AutoSort will come out of 'training mode', and automatically sort any incoming messages, once more than 15 emails have been moved out of the Undecided area into another non-spam area.

Example:
This is easily explained with an example. Imagine you have just set up a mailbox and Inbox project with the following areas:

Area Spam Not Spam Undecided Monkeys Zebras # of Email 0 0 0 0 0 NOT sorting - in training

Since you have not received any email yet, FogBugz AutoSort is in 'training mode' and places every incoming message into Undecided. If you receive 20 emails:

Area Spam Not Spam Undecided Monkeys Zebras # of Email 0 0 20 0 0 NOT sorting - in training

Now, you manually move these messages into their appropriate areas:

Area Spam Not Spam Undecided Monkeys Zebras # of Email 5 5 0 10 0 AutoSorting - done training

The total number of emails in categories other than Spam and Undecided is at least 15, so FogBugz AutoSort will start to automatically categorize the next incoming message.

However, if you were to change your mind and move one of these cases around such that:

Area Spam Not Spam Undecided Monkeys Zebras # of Email 6 5 0 9 0 NOT sorting - in training

...then FogBugz AutoSort would return to 'training mode' and place all incoming messages into Undecided until you moved another email into Not Spam, Monkeys, Zebras, or any other category except Spam and Undecided.

NOTE: this means that even if you have received over 500 emails and diligently moved them as such:

Area Spam Not Spam Undecided # of Email 500 14 0 NOT sorting - in training

...FogBugz AutoSort will still be in 'training mode' because it is below the 15 message threshold.

"Why all this nonsense about 15? Just have it start sorting immediately!" you say.

This feature is implemented in order to guarantee that FogBugz AutoSort has sufficient knowledge of your email (not including spam) so that there is minimal chance of a non-spam message being automatically categorized as spam. When we say "your email" we mean do mean "your", and that's the whole point of Bayesian spam filtering. Here at Fog Creek, the word "mortgage" has surely somewhere around a 99.9% likelihood of residing in an email that is spam. However, if you're using FogBugz in the IT department of a mortgage lender, the word "mortgage" for all intents and purposes reveals nothing about whether or not the email that contains it is spam.