ISSUE
When attempting to email any mailbox which is hosted in O365 where a hybrid (co-existence) configuration has been deployed with an on-premise Exchange 2003 organisation you receive NDR email messages and event log errors are raised as follows:
EVENT LOG:
Event Type: Error
Event Source: MSExchangeTransport
Event Category: NDR
Event ID: 3020
Date: 12/13/2011
Time: 11:12:28 AM
User: N/A
Computer: SERVER
Description:
A non-delivery report with a status code of 5.4.6 was generated for recipient x-ex;/O=EXCHANGE/OU=External (FYDIBOHF25SPDLT)/cn=Recipients/cn=61338b4fc700481296869bdf761c0edb (Message-ID <3DA1FDF3A7EA5C4DBD3E3F0AE3553B81788AFB@server.domain.local>).
Cause: A forward loop was detected by the categorizer. This is a common hosting configuration problem caused when someone uses the provisioning tool to create a contact in one organization unit and creates a user in a different organization user that share the same e-mail address.
Solution: Verify that you do not have a user in organizational unit and a contact in a different organizational unit that have the same e-mail address.
Data:
0000: 46 05 04 80 F..
Email NDR:
Subject: Test
Sent: 13/12/2011 11:39
The following recipient(s) could not be reached:
ADMIN1 on 13/12/2011 11:39
A configuration error in the e-mail system caused the message to bounce between two servers or to be forwarded between two recipients. Contact your administrator.
<server.domain.local #5.4.6>
Resolution
This error normally occurs because the email policy for the service domain in Exchange 2003 has been misconfigured.
To resolve the issue run through the following:
- In Exchange System Manager, navigate to Administrative Groups > Recipients > Recipients Policies
- Open the Recipient policy which contains the service domain name (normally in Default Policy)
- Select the E-Mail Addresses (Policy tab) edit the SMTP addresses used by the service domain name (I.E service.domain.com, %g.%s@service.domain.com)
- Uncheck This Exchange Organization is responsible for all mail delivery to this address.
- Click OK and Close Exchange System Manager
Wait for AD and the Email Policy to synchronise
Then confirm that emails can now be sent to O365