shared mailbox access per group

Dear all,

with reference to

https://technet.microsoft.com/en-us/library/jj919240(v=exchg.150).aspx

I tried to add a Group Level permission to my Shared Mailbox. So I went to powershell, added the snapins and ran the cmdlets, like that

$organizationalunitpathusers  = "OU=Shared Mailboxes,OU=Accounts,DC=mydomain,DC=src"
$organizationalunitpathgroups = "OU=Distribution Group,OU=Accounts,DC=mydomain,DC=src"
$domaincontroller = "dc01.mydomain.src"

new-mailbox -Name $username -OrganizationalUnit $organizationalunitpath -DisplayName $username -UserPrincipalName "$username@mydomain.com" -Room -domaincontroller $domaincontroller


new-distributiongroup -name "$username-fullaccess" -OrganizationalUnit $organizationalunitpathgroups -domaincontroller $domaincontroller
set-distributiongroup "$username-fullaccess" -managedby $listmanager -domaincontroller $domaincontroller
add-mailboxpermission $username -user "$username-fullaccess" -accessrights FullAccess -domaincontroller $domaincontroller

I can see the Mailbox $username and the distributuion Group is created fine. I can also find the mailboxpermission set when running get-mailboxpermission. As I know there is a cached ACL in Exchange I did wait some hours (days, as I am not workiing constantly on this issue), but it seems the permission is not working. when I checkedby using a mailbox member of the"$username-fullaccess" Group, there was no automapping in Outlook and also no access permission (a Client Operation failed) when I tried to Access manually via Outlook or OWA.

When I double-checked the Technet article mentioned before I expected that to work like in Exchange 2010.

Can you tell me what I did wrong / what I am missing to get access?

Thanks in advance.

Regards,
Martin