Because automapping is not always working correct, just created this script to re-enable automapping with the correct settings. This script you need to run on the Exchange server.
# Created by Daag van der Meer
# blog.van-daag.nl
# This script gives the user full access to the mailbox. This will update also the folders below the inbox with the rights.
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn;
# Enter the mailbox name here
$mailbox= "<mailboxname>"
# Add here the usernames like "<USERNAME>", "<ÜSERNAME>"
$users= "<USERNAME>", "<ÜSERNAME>"
####### Start of the Script. Do not edit below
foreach ($user in $users){
# First disable AutoMapping
Add-MailboxPermission -Identity $mailbox -User $user -AccessRights FullAccess -InheritanceType All -Automapping $false
# Now enable Automapping
Add-MailboxPermission -Identity $mailbox -User $user -AccessRights FullAccess -InheritanceType All -Automapping $true
}