As I've mentioned before, there is a two-step rule which will move 98% of your Spam to Junk Mail. The rule needs to state that a piece of mail which is in HTML Format, and whose sender is not in your address book, gets moved to Junk.
You still need to review Junk for mail fom new correspondents, or old ones using different addresses. But this is rare, at least for a personal mail system. for the library, where you expect mail from strangers, it would be less effective but it is still true that they have little need or probability of sending mail in HTML format.