You can still use SpamSieve with mail programs that are not directly supported. To do this, configure Apple Mail to access your mail account and then follow the normal SpamSieve setup instructions in the Setting Up Apple Mail section. SpamSieve will then filter your Web mail when Apple Mail is running. It can run in the background—and you can hide its windows if desired—while you use your preferred mail client to perform your normal e-mail tasks. (To do this automatically, you can set up Apple Mail in System Settings ‣ General ‣ Login Items.)
You can train SpamSieve from within Apple Mail or from SpamSieve’s Log window, or use the drone setup to train SpamSieve from your primary mail client by moving messages into the special training mailboxes.