Help with shared domain onpremise - Office365(Exchange)

Hi everyone. I have a shared domain between my on premise server ( sendmail) and my office365 tenant with Exchange.

The real mailbox is on premise but I have enable Outlook to have a calendar in Office365. The problem is when a email is sended between users of the same domain in Exchange, for instance from owa I want to send a email, from mailto:pepe@shareddomain.es to mailto:juan@shareddomain.es, this message is delivered into Exchange because it´s the domain of the tenant, but I want to will send to my onpremise email.. What can I do?. Any help will be appreciated.. 

Thxs in advance.