Answer: I would suggest you check with a drainage expert, there may be a way to redirect the runoff from your neighbor's yard so it does not flood your crawl space. This might involve creating swales or installing drains, sometimes it is not that expensive to do. In any case it is probably a good idea to fix it if at all possible to avoid structural problems with your house and foundation beyond the mold or mildew you notice already. A professionally trained landscape architect or other professional with experience in this type of problem should be able to make suggestions based on a site visit. Good luck!
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