Access shared online exchange mailboxes from an onPrem exchange email account


we have several users having an onPrem exchange email mailbox.
On the same time we are using also online exchange mailboxes. Some of these online exchange mailboxes are shared mailboxes and given access also to the onPrem users.

With Outlook we could access with a onPrem user to the shared online mailboxes.

With eMClient this is not working. Even so we do find the shared mailboxes in the delegation menu and can add them, but they will not show in the client itself.

Anybody has a solution for that?