As for the Epistles, most scholars agree that Romans, 1 & 2 Corinthians, Galatians, and Philippians were definitely written by Paul. There is disagreement among scholars on teh authorship of Ephesians, Colossians, 1& 2 Thessalonians, Philemon, 1 & 2 Timothy, and Titus. The latter three are generally regarded as pseudepigraphical works. Most scholars reject the idea that Paul is the author of Hebrews.
Do me a favor...open your Bible (you have one, right?) and read the first few verses of the first chapter of each of those books. They ALL start out identifying Paul, himself, as the writer. As to your "generally regarded" statement, I'd have to ask, by whom?, as it really is generally regarded as Paul being the author since he identifies himself at the start. Whether or not an associate of Paul maybe being the secretary writing down what Paul says, is a possibility, but the autograph IS from Paul...every one. Another point is that the early churches would have known what letters they got and from whom they came as the Apostles had emissaries as well as personally delivering some of the epistles. From the start, the Christians knew and accepted the authority of the Apostles and received their writings AS Scripture. Any suggestion that an author was unknown is preposterous as the believers would NOT have received letters from anonymous writers. Didn't happen.