Michael Tsai, contradicting foolish advice from others that you shouldn’t mark certain spams as spam, lest you confuse your spam filter:
In both cases, my recommendation is simple: tell SpamSieve the truth. If a message is spam, train it as such; don’t omit a message because you think it will confuse SpamSieve. This is for two reasons. First, there’s probably some spammy content that SpamSieve could learn from, even if it doesn’t appear so. Second, if you don’t train the message as spam, SpamSieve will assume that the message was good and that you want to see more such messages.