Hey Florian!
You can reach out to them via the Yahoo Sender Hub>>Contact>>Problems Delivering Mails.
That being said, I wouldn't put a ton of emphasis on inbox placement tools, and it's unlikely that mail is going to spam for a technical reason that they could repair. More likely, it's due to sender reputation which takes things like bounces, complaints, and engagement into account.
- Are you generating spam complaints at Yahoo?
- If so, what rates are you seeing?
- How do people sign up for your emails?
- Single or double/confirmed opt-in?
- When do unengaged users get excluded from mailings?
Looking forward to learning more!
