A couple of months after an Exchange 2003 to Exchange 2010 migration any email enabled public folders that had been working just fine after the migration would stop working. NDR would be like:
#< #5.2.0 smtp;554 5.2.0 STOREDRV.Deliver.Exception:ObjectNotFoundException; Failed to process message due to a permanent exception with message The Active Directory user wasn’t found. ObjectNotFoundException: The Active Directory user wasn’t found.> #SMTP#
Determined after research that I needed to delete the cn=servers container under .cn=first administrative goup.cn=Administrative Groups.CN=domainname.Microsoft Exchange.cn=Services.cn=configuration
This page helped out:
Mail started working about 20 minutes or so after removing the servers container… no restart required.