Clear Submission Queue on Microsoft Exchange Server 2007 / 2010 | Remove message from queue on Hub Transport Server | Delete ambigous messages from submission queue | Emails are stuck in the Exchange Server queue | Troubleshooting Exchange Queue

Author: Zahir Hussain Shah | MVP Exchange Server, CISSP

Troubleshooting Microsoft Exchange HUB Transport Server (Transport Queues)

Often due to loss of Internet connectivity and DNS name resolution issues, we run into a situation, where we see a big count of e-mails get stuck at Exchange HUB Transport Server queue, usually these e-mails get stuck at your smart-host connector, which is the next-hop for your e-mails, but sometimes, due to some conflicts and other issues, we see e-mails get stuck in the Exchange Hub Transport Server for different queues, instead of the one, which is bound with your smart-host, for an example, lets say if you are using FOPE (Microsoft Forefront Online Protection for Exchange Online Service), then in this case, you will see emails getting stuck at (SmartHostConnectorDelivery).

Okay, we said something about the queues, now let me drive your attention towards the goal of this blog post, where I will guide you the basic troubleshooting for your Exchange Hub Transport Server and its queue.

Here are few of the common issues with Microsoft Exchange Hub Transport Server and its queues:


1) E-mails get stuck at the SmartHostConnectorDelivery for out-bound e-mail delivery

2) Last Error: A matching connector cannot be found to route the external recipient

3) Last Error: 420 4.2.0 RESOLVER.ADR.Ambiguous; ambiguous address / Large number of messages get stuck at submission queue


E-mails get stuck at the SmartHostConnectorDelivery for out-bound e-mail delivery Issue:

For this type of problem, usually the cause is the loss of connectivity with Internet or with the HUB Site, which is responsible for routing e-mails to the appropriate destination (commonly to the Internet), and sometimes, it happens due to the bad DNS cache, which does not allow you to connect with the Smart-Host for the email delivery, and also the authentication which plays a vital part for allowing your HUB Transport Server to connect with remote-smart-host for delivering e-mails.

You can use the below solutions to fix this type of issues with e-mail delivery:

–>> Fix the IP connectivity issues for Internet / remote smart-host.

–>> Clear the DNS cache on DNS Servers and Exchange Hub Transport Servers (IPconfig /flushdns).

–>> Based on your remote-smart-host authentication requirements, set the appropriate authentication providers on your Send-Connector.

Last Error: A matching connector cannot be found to route the external recipient:

As it sounds with its name that the corresponding or matching send-connector is missing from Exchange HUB Transport Configuration, and for fixing this problem, you can create a send connector for the similar SMTP Address Space, but if you want to create a single SMTP connector for all type of domains, then make sure that you create *, a wild-card based SMTP connector, so all emails for any destination will be routed through this send-connector:

Last Error: 420 4.2.0 RESOLVER.ADR.Ambiguous; ambiguous address / Large number of messages get stuck at Submission Queue

This type of situation happens, when you perform some type of activity, which in result conflict the LegacyExchangeDN attribute on Exchange Server, (for reading more about legacyExchangeDN, read the below links), in this case, Exchange Server cannot decide where to send email for the particular legacyExchagneDN value, where the same value being used for either two different Mail-Enabled Users (Mailboxes) or between Mail-Enabled User (Mailbox) and Mail-Enabled Contact, in this situation, this emails will always stay at the Exchange Submission Queue, and you will constantly will receive the below errors in the Exchange Hub Transport Server event viewer:

Messages stuck at Submission Queue on Exchange Hub Transport Server:

Question: Okay, since these are ambiguous messages, which got created when there is a conflict of LegacyExchangeDN, now I have fixed it, so how can I remove these messages, because they are logging the above shown error log in me Exchange Hub Transport Servers event viewer?, well unfortunately, there is no way to delete messages from Exchange Management Console in both Exchange 2007 / 2010, and recently, while working for one case with Microsoft Support for Exchange Team, where I asked them can I delete these messages, so they told me the ONLY way to delete these ambiguous message from Exchange HUB Submission Queue, you have to Stop the Microsoft Exchange Transport Service, on Exchange Hub Transport Server, where the messages are stuck in the submission queue, and then rename the C:Program FilesMicrosoftExchange ServerV14TransportRolesdata” data folder to Data_OLD, and then start the “Transport Service”, which will recreate the “Data” folder, with fresh database for queue and other required files and folders, so this way you can delete these messages, and which sounded quite annoyed to me, that renaming these type of folders, is not a good idea, so I started looking for a solution, where I can delete these messages from Exchange Management Shell.

And a good thing that when I looked at the possibility for deleting these messages from EMS, so I found that it is pretty straight forward and easy, so lets see how you can delete them from Exchange Management Shell in both Exchange 2007 / Exchange 2010:

[PS] C:Windowssystem32>Get-Queue -id Submission | Get-Message | Remove-Message -WithNDR $false

Where in the above CMDLet WithNDR $false is telling the Exchange Server that dont send NDR to the original senders of the email, so you can scilently remove these messages from your Exchange without letting your end-users know.

In addition to the above CMDLet, you can use the same CMDLet for other queues, which are getting generate in your Exchange Hub Transport Server, for knowing about the Exchange Hub Transport Queue, you can run the below CMDLet:

[PS] C:Windowssystem32>Get-Queue 

Identity                                    DeliveryType Status MessageCount NextHopDomain——–                                    ———— —— ———— ————-Server_Name\Submission                             Undefined    Ready  0            Submission

Server_Name \Unreachable                            Unreachable  Ready  1            Unreachable Domain

To know more about LegacyExchangeDN, see the below links:

Update legacyExchagneDN attribute for Mail-Enabled Contacts

GAL Sync issues for LegacyExchangeDN
This blog post will enable you to manage and troubleshoot your Exchange Hub Transport Server and it’s queue efficiently.



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About Zahir Hussain Shah

Systems Infrastructure Consultant, Systems Solution Architect, Senior Systems Engineer. Certifications: MCSE, MCTIP Entperprise Administrat

Posted on 13/03/2012, in Active Directory, ActiveSync, AD DS, ADModify, Exchange 2007, Exchange 2010, GAL Sync, NDR, Outlook, Windows 8, Windows Server 2008 R2, Windows Server 8, Windows7 and tagged , , , , , , , , . Bookmark the permalink. 6 Comments.

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