Event ID 9041, An exception has been thrown: Microsoft Exchange Assistants TransientMailboxException

I recently encountered a mail flow problem between two of my test lab environments that was being caused by the DNS configuration on the receiving server’s network interface.

While I was trying to send email from organization A to organization B, the emails were queuing on the organization A transport servers with the following error:

451 4.7.0 Temporary server error. Please try again later. PRX2

Here’s the full Exchange management shell output:

[PS] C:\>get-queue ex2016srv2\11 | Get-Message | fl
RunspaceId                      : 524470e8-3e28-4260-8f5b-64c4749244af
Subject                         : Test 2
InternetMessageId               : <564407fa60df4720851f66fc31dabb8a@EX2013SRV1.exchangeserverpro.net>
FromAddress                     : Alan.Reid@exchangeserverpro.net
Status                          : Retry
Size                            : 6.833 KB (6,997 bytes)
MessageSourceName               : SMTP:Default EX2016SRV2
SourceIP                        : 10.1.4.30
SCL                             : -1
DateReceived                    : 6/01/2016 2:25:41 PM
ExpirationTime                  : 8/01/2016 2:25:41 PM
LastError                       : 451 4.7.0 Temporary server error. Please try again later. PRX2
RetryCount                      : 1
Recipients                      : {administrator@exchange2016demo.com;3;2;[{LRT=};{LED=451 4.7.0 Temporary server
                                  error. Please try again later. PRX2 };{FQDN=};{IP=}];0;CN=To Partner Company
                                  2,CN=Connections,CN=Exchange Routing Group (DWBGZMFD01QNBJR),CN=Routing
                                  Groups,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative
                                  Groups,CN=Exchange Server Pro,CN=Microsoft
                                  Exchange,CN=Services,CN=Configuration,DC=exchangeserverpro,DC=net;0}

What I found interesting was that internal mail flow for organization B was not working either. On closer inspection of that Exchange server I found the following Application event log entry repeating every 5 seconds or so.

Log Name:      Application
Source:        MSExchange Assistants
Date:          1/6/2016 4:05:17 PM
Event ID:      9041
Task Category: Assistants
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:      DEMOEX16.exchange2016demo.com
Description:
Service MSExchangeSubmission.  An exception has been thrown: Microsoft.Exchange.Assistants.TransientMailboxException
   at Microsoft.Exchange.Assistants.Util.TraceAndThrow(Action function, AIException aiException, String nonLocalizedAssistantName)
   at Microsoft.Exchange.Assistants.Util.CatchMeIfYouCan(Boolean translateToPermanentException, Action function, String nonLocalizedAssistantName, ISet`1 permanentExceptions)
   at Microsoft.Exchange.Assistants.Base.CatchMeIfYouCan(Boolean translateToPermanentException, Action function, String nonLocalizedAssistantName, ISet`1 permanentExceptions)

The server happened to be running the Preview release of Exchange 2016, so I took the time to perform an upgrade to Exchange 2016 RTM before anything else. When the problem persisted, I dug further and found that I had configured the network interface on the server with a secondary DNS of the IP address of my home router.

event-id-9041-network-configuration