Shared Mailbox - Mark as read for all users

Shared Mailbox - Mark as read for all users

Hi all,

Maybe someone can help me out. At the moment we have a shared mailbox without streams.
When a users reads an mail or marks it as read other users will not see this. 
How can we resolve this? We now archive the mails when read and followed up. 
However in this method the e-mails keep being unread to other users.

Hope someone can help me out.