create new shared inbox in office 365 in hybrid envrioment

we are nearing the end of a migration to 365 using a hybrid setup.  

when i set up new resources in 365, lets say a new shared inbox.  how do i let the on prem exchange server know about it.  My understanding is at some port of the migration contacts get setup on my on perm exchange server that helps to redirect emails to the 365 environment.  But when i setup lets just say a new shared inbox in 365, then items in the old environment are unable to deliver as the contact never gets build.  

Note that i have an on prem exchange 2010 server.  

Thanks,