Unfortunately the inbox delivery is out of our "direct" control since it has to do with the clients email system, firewall etc.
We keep doing what we can to improve delivery to the inbox.
It helps to inform your clients before hand so that they can mark your email as not spam which in turn will mark our domain 'planiteasy.com' as safe.
This will move all the future messages to their inbox.
We are working on a domain masking feature, which will replace our domain with your domain, that could also potentially help delivery success to the inbox.