Zoho Mail Mobile app and IP restrictions

Zoho Mail Mobile app and IP restrictions

We have a problem. We have used Zoho Mail and other products for many years. We enjoy being able to lock down users based on IP addresses. Unfortunately it has now come to our attention that it appears a Zoho user, regardless of any IP restrictions we set, can access and send mail from the Zoho Mail mobile app. Is there a way to stop this? We see this is a bad security issue. Please let us know how we can prevent this as soon as possible.