Tests pass

src/Data/Email/Header.hs

@@ -41,6 +41,7 @@ decode = parseOnly parseHeader
       name <- T.pack <$> many' (notChar '@')
       _ <- char '@'
       rest <- T.pack <$> many' (satisfy (\c -> not (isSpace c) && c /= ','))
+      _ <- many' (notChar ',')
       pure (name <> "@" <> rest)