In a nonreactive container, combine cabbage, peppers, and onions. Sprinkle with salt, and toss to combine. Cover, and refrigerate overnight.
Remove cabbage mixture from refrigerator, and drain, discarding liquid. Rinse cabbage mixture with cold water, and drain again. Transfer cabbage to a large saucepan. Place spices (allspice, bay leaf, cinnamon stick, cardamom pods, and star anise) in a square of cheesecloth, and tie with kitchen twine. Add sachet to cabbage mixture. Combine vinegar and sugar in a liquid-measuring cup. Pour over cabbage mixture, and stir to combine. Bring to a boil. Reduce heat to simmer, and cook, stirring occasionally, for 20 minutes. Remove and discard sachet.
Ladle relish into jars. Cool on a wire rack to room temperature. Cover, and refrigerate for up to 2 weeks.