# Junk Email (Spam) Filtering

This option filters messages based on how much they look like junk email (otherwise known as spam) according to a score that is computed by applying a large number of tests to each message and calculating an overall result. Since it isn't possible to decide on technical grounds precisely whether an email is spam or not, the score is heuristic: a higher score means the message is more likely to be spam.

You pick a threshold score above which messages are filtered to a separate spam folder, which you should check periodically (once a week, say) for misfiled email and to delete all the spam. The lower the threshold the more likely it is to misclassify a legitimate message as spam, so a score of 1 is likely to move genuine messages to your spam folder and a score of 20 is likely to leave spam in your inbox.

We recommend setting the threshold to 10 at first, and adjusting it based on how well it works for you. Note that the filter is most accurate for English email so if you exchange a lot of foreign-language email you will probably have to use a higher threshold.

The purge option (if available and enabled) defines the number of days that mail remains in your spam folder before it is automatically deleted by an overnight job. The default is 60 days.

The whitelist section is a list of sender addresses (one on each line) which will bypass the spam filter. Wildcard characters are allowed: '?' matches any single character, while '*' matches any number of characters