One address, read regularly:
Bug reports about the validator itself. If a run stops, returns something odd, or misses a section of your site, tell us the address you entered and roughly what happened, and we can usually reproduce it from there.
Mistakes in our pages, whether a typo, a technical claim that has aged badly, or an example that no longer reflects the current specification. Corrections are applied and appreciated.
Questions about validation that deserve a proper answer. The recurring ones end up on the FAQ, which is how that page grew in the first place.
We do not fix websites. The tool locates errors and links to reports explaining each one, and that is where our involvement ends. For a page you cannot untangle, the detailed report plus our common errors reference will get you most of the way.
We cannot check private or local sites on your behalf, for the reasons explained in the FAQ, and we do not keep any record of past runs, so we cannot retrieve results from yesterday.