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Corrections, questions and suggestions all go to the same place, and all of them are read.
The most useful message you can send is a correction with a primary source attached. Those get acted on quickly and are published on the page they affect.
Questions about a specific site's problem are welcome, though the honest answer is often that the diagnosis needs your server logs and Search Console data rather than a description. The fifteen-step checklist on the homepage resolves most of them faster than a reply would.
Guest post pitches, link exchanges and paid placement offers are declined automatically and are not read.