I still don't know why we have to use old webmail in order to modify delegation. If a user wants to delegate calendar permissions, but does not want to give them access to the inbox (you can do this, and it new calendar events are properly shown in the calendar), you have to do the following:
In order to do delegation without inbox sharing, in the case of "User A" delegating their calendar management to "User B" please do the following:
1) From User A's Kerio, go into kerio connect (new webmail), settings, delegation, add "User B".
2) Then, still from User A's Kerio, go into old wabmail, right click on the inbox, click access rights, select and delete "User B".
I even wrote a powershell script to report inbox over-sharing.
I thought it already does this.
Accounts->Groups->Add->Add from Directory Service.
You can search "All Folders", just add a similar option of "all subfolders" in the same spot.