I'm not a Bible expert (I say that a lot haha), but if I'm not mistaken, Hebrews is the only epistle whose authorship is uncertain. Even though it's commonly attributed to Paul, most scholars don't believe it, because its style differs so much from the ones we "know" he wrote:
Romans, 1 & 2 Corinthians, Galatians, Ephesians, Philippians, Colossians, 1 & 2 Thessalonians, 1 & 2 Timothy, Titus, and Philemon.
I put "know" in parenthesis because many scholars will say we have no concrete proof Paul actually wrote any of those, but agree that at least seven are genuine - Romans, 1 & 2 Corinthians, Philemon, 1 Thessalonians, Galatians, and Philippians. However, we also have no proof that Shakespeare actually wrote his plays. And there's less proof of the existence of Alexander the Great than there is that Paul wrote the epistles. Sorry to swerve off topic but had to put my two cents in there. ;)
Basically, it's commonly accepted that Paul wrote 13 epistles. Hebrews (contested), James, 1 & 2 Peter, 1, 2, & 3 John, Jude, and Revelation are the only ones he didn't write.
Sorry I drug that out more than was necessary, but hope that helped. Blessings.