What does the -u (autoupdate) switch do?
The “-u” switch (autoupdate) is used to automatically expand the wordlist. When this switch is used and bogofilter classifies a message as Spam or Ham, the message’s tokens are added to the wordlist with a ham/spam tag (as appropriate). As an example, suppose a new “Refinance now – best Mortgage rates” message comes in. It will have some words that bogofilter has seen and (probably) some new ones as well. Using ‘-u’ the new words will be added to the wordlist so that bogofilter can better recognize the next, related message. If/when you use to use ‘-u’, you need to be on the lookout for classification errors and retrain bogofilter with any messages that have been classified incorrectly. An incorrectly classified message that is auto-updated _may_ cause bogofilter to make additional classification errors in the future. This is the same problem as when you (the sys admin) incorrectly register a ham message as spam (or vice versa).
