Change language
I think everybody knows how much spam appear on league messageboards, but the worst fact is that this spam is undeletable as far as message author dosn't want to delete it (or we write to support, which has many more important tasks to do). I think all he ideas of "vote deleting" or something are bad from the beginning, because they need engagement of league members, which may be high in high leagues, but in low leagues it nearly don;t exist. Thus I had a bit brutal, but a very effective idea: make writing on message boads of all leagues but your own impossible.
The truth can be seen very easily: if somebody writes something on message board of league which is not his own league, it's almost always spam. Most of players are uninterested in results, discussions etc. of other leagues (maybe excluding highest ones or situations when you have e.g. friend in this league), thus they just don't write on them as far as they don't have interest in it (and interest = advert player or - especially last days - promoting candidate in NC election). Per 1000 messages on league boards written by players not from this league maybe 1, 2, 3, at most 10 (I don't know statistics) is not spam. I think so low amount of "normal" messages is not worth as much as freedom of spam. And there is still possibility to talk by guestbooks anyway (where spam is not a problem, because you can just delete it).
This change would once and forever finish an issue of message boards spam. As I said - maybe this method is brutal, but I don't think something better and still effective can be proposed. Because as far as writing mesages is possible, some people will use it to spam, no matter what the rules will be.