Exchange Server 2010 to 2016 upgrade - GetSharedMailbox

We are upgrading our Exchange Server from 2010 to 2016 and have some issues changing our redemption code. What we do with Exchange Server 2010 is: LogonExchangeMailbox (with a user that has access to other mailboxes) GetSharedMailbox (mailbox that we want to send the mails from) GetDefaultFolder(16):Items:Add from that mailbox

As Exchange Server 2016 only support RPC-over-HTTP, we have change to LogonHostedExchangeMailbox (which forces us to code the password for the service user) to connect to the service user mailbox. After this change the GetSharedMailBox works for mailboxes still on Exchange Server 2010, but not for mailboxes already migrated to Exchange Server 2016. In that case I get this error:

Error in IMAPISession::OpenMsgStore(pbExchangeProvicderPrimaryUserDuid): MAPI_E_FAILONEPROVIDER Error code: 0X80020009

What is the correct way to do GetSharedMailbox for a mailbox hosted on Exchange Server 2016?