Email, Messaging, & Video Calls > Email Configure the K9 Spam Email Filter By Heinz Tschabitscher Heinz Tschabitscher Writer University of Vienna A former freelance contributor who has reviewed hundreds of email programs and services since 1997. lifewire's editorial guidelines Updated on October 17, 2019 Tweet Share Email Tweet Share Email Email Yahoo! Mail Gmail After you have trained it a bit, K9 knows spam from good mail pretty precisely. But if only K9 knows the benefit for you is negligible. Training K9 There must be a way for K9 to communicate this knowledge about spam to you -- or your email client for automatic filtering. As it turns out, there is more than one way. You can have K9 mark spam in the Subject so you can spot it at a glance. This Subject-line marking is also useful if you use an email client that can only filter on a few header lines (Outlook Express for example). If you want to have junk mail moved to a special folder silently, you can tell K9 to add a custom header line to messages it identifies as spam. Then your email client can filter mail based on this line. To Configure How K9 Marks Spam Open K9.Go to the Configuration tab.Select the desired marking method under Mark emails as Spam by... Was this page helpful? Thanks for letting us know! Get the Latest Tech News Delivered Every Day Subscribe Tell us why! Other Not enough details Hard to understand Submit