Spam protection is done by you specifying what keywords aren't allowed in issues or followups. If there's a match on any of the keywords you specify here, the issue or the follow will not be saved.
You write one keyword per line. A keyword can contain spaces. Any duplicates or blank are filtered out when you save.
Combinations and subwords are entered like this: you write first the keyword and then all subwords on the following lines but add a bit of whitespace before the words to indicate the relationship of the first keyword. Combinations are matched if the first word (no whitespace to the left) is found and the any of the following words appear. This is useful if you want to flag up two offending words who on their own are harmless but together is considered spam. It doesn't matter who many spaces you put in front of a subword. All text matching is done case insensitively.