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Walkthrough Wednesdays

Unity Connection 8.5.1 Single Inbox (Unified Messaging) Forward/Reply in Outlook fails with NDR

Tray Stoutmeyer
Cisco Employee

We are getting a number of TAC cases where customers are setting up single inbox feature (unified messaging) with where they try to reply  to or forward a voicemail via Outlook e-mail and receive an NDR message in return. First let me try to explain why this will fail the way it does and then try to supply some direction for your Exchange admins to make this work in your current environment.

Why this fails:

It is basic mail routing/addressing. When you have single inbox setup on CUC, part of that setup is a CUC SMTP DOMAIN. Typically this should not match your corporate mail domain. This is now documented here...

It is usually just the hostname of the CUC server out of the box but some like to change it to something that resembles and actual domain. For our purposes here, we will use CUCSMTPDOMAIN.ORG for example. For the corporate domain, we will use CORP.COM for example. Let's go over the scenario.

UserA on CUC sends a voicemail to UserB. This voicemail arrives on UserB's Outlook via the Single Inbox Synch. We would expect the UserB to use VMO or TUI to reply to the voicemail in a CUC environment but many users whom have come from a Unity system to a CUC system via migration don't realize this is the method preferred and used the simple reply/forwards via Outlook while on Unity previously. This no longer works in CUC. This is why. When UserA on CUC sends the voicemail to UserB on CUC, it will be addressed as FROM  UserA@ CUCSMTPDOMAIN.ORG and will arrive in the Outlook of UserB with the same FROM address. If the UserB uses VMO or TUI for reply/forward, the message will send without incident. If UserB uses Outlook e-mail client to reply or forward, a NDR will be generated and the message send will fail. Why is this? When you use VMO, it talks directly to CUC where  UserA@ CUCSMTPDOMAIN.ORG will be resolved and delivered correctly. If VMO is not used, Outlook talks to the corporate Exchange server where it has no clue what or where CUCSMTPDOMAIN.ORG is or whom resides there. Thus the NDR is generated when attempting this. It's a simple matter of not being able to resolve the user you are trying to reply to because you are talking to Exchange on the corporate domain and telling it to deliver a message to a domain is can't resolve. From the NDR, you can see it typically talks about a lack of an MX record or the like or not being able to resolve the address. From the customer interactions I have had, there seems to be a few fixes for this I wanted to share here. Granted TAC is not responsible for configuring a corporate Exchange environment for this but at least this might help your Exchange admins figure out what to do to fix the issue. This is not a step-by-step fix.

Possible Fixes:

In the exchange 2010 environment you have to setup an “internal relay domain” and point it to route the mail destined for that domain to the unity connection server. 

For Exchange 2003 you need to create a connector with the address space of the destination domain and have it route to the unity server.

There may be some additional configurations, depending on what you want to happen once the mails are delivered to the CUC users but I will point you to a very nice post here from David Hailey to fill in that info. It also has more details as to why these messages are treated differently depending on method of reply and forward.

I hope this helps anyone struggling with this issue with our new feature. Just keep in mind, using VMO and/or TUI to reply will take care of this as it was the intended method with CUC. At the same time, I see that in previous Unity deployments, users used Outlook reply/forward all the time and would like to continue having the ability after being migrated to CUC Single Inbox.

I would add this as well since this is getting really good traffic on the forums.

It explains a bit more what the behavior is and why, without installing the VMO client, UM forwarding/replying etc. will not work like old Unity UM did.

Please feel free to comment or add to this post.


Excellent information.

Before this post I had been troubleshooting this exact scenario.  I had resolved it by making the SMTP Domain on the Unity Connection Server match the Exchange Environment.  I also verified that the primary SMTP address on the each user matched the SMTP address in Exchange.  That enabled users to freely reply/forward .wav attachements.  It seems to be working fine but you had mentioned "Typically this should not match your corporate mail domain".  Could you explain why this is the case?




"For Exchange 2003 you need to create a connector with the address space of the destination domain and have it route to the unity server".

Can someone please elaborate on this?  We have UC 8.5 SU1 and we have created a connector on the exchange side with the addresses of all of the unity servers, but we still can not get this to work.  Each user has the SMTP address for their exchange account configured in Connection. 

We have 65,000 users so were hoping that we did not need to add the SMTP domain as an email address to each users AD exchange addresses, which I know works, but is this the only way to achieve this? 

Bradford Magnani
Cisco Employee


This link looks like it is pretty useful with a step-by-step process of how to create a connector:

Hope that helps,


Bradford Magnani
Cisco Employee

Hi Shane,

It was recommended by development not to have two entities in your environment thinking they own the same SMTP domain as NDRs, notifications, etc. can potentially get lost/mis-delivered to the wrong domain (AD vs. UC).  Other than that, if your system is working properly with no issues, it's probably safe to leave the way it is.

Hope that helps,



Wow is that  a poor design. You really can't call it single inbox if voice mails come from a different address. As a 7 year multi-tenant unity user this is disheartening. A lot of companies don't whish to install VMO on their outlook client's and you shouldn't have to if this is truley "single-inbox". Not to mention VMO does not address OWA or active sync users. Hope you fix this soon, this is a step back from Unity. Why not just send the emails from UCXN to exchange from corporate email address ? Come on its 2011 guys

Steve Bethea

How is this rant helpful in any way?


What?  It's valid negative feedback for a decision on Cisco's part to create an incompatibility with typical Exchange operation and then not create clear, documented assistance in dealing with the issue.  I concur completely with the sentiment; it exactly matches the experience we have had.  If they're going to employ a Single Inbox environment, then write the product in such a way as to be easily integrated into that environment or publish competent documentation on alternative configurations.  It's not and Cisco didn't.

The _assumption_ that VMO will be used ("We would expect the UserB to use VMO") is utterly arrogant.  I have attempted to use VMO many times in the past.  It works for a short while, then fails with an Outlook form error and reverts back to .WAV attachments.  I don't know why it fails, but it has exhibited this behavior at our site for several years and versions of it, Outlook and Exchange.

No amount of remediation has solved the problem.  Uninstalling and reinstalling VMO & Outlook or recreating the mail profile do not correct the situation.  Cisco can't seem to fix the issue either only responding with the patheticly patronizing suggestion to wait until the next VMO release.  Only when a brand new PC with completely new install of Outlook is used does VMO work.... for a short while, then fails.  If VMO use is "expected" as stated above, then Cisco better damn well make sure it's resilient and works consistently.

Tray Stoutmeyer
Cisco Employee

This is a bu recommendation in that it can break other features down the road if you plan to use them...

1)      You will likely not be able to route messages between nodes in a

Digital network.

2)      Relay'ing of messages may not won't work properly.

3)      NDR's to connection messages may get lost.

Certainly if you have no plans to bother with any of these, then this will allow this to work as you stated. Otherwise, this is why the bu recommendation is to not have your SMTP domain match your Exchange/AD domain.


David Cebula

We got bitten by the same gotcha in our Unity 5.x to UC 8.5 migration. We addressed the NDR problem by making the UC SMTP domain a subdomain ( and having Exchange retain (

This works, but still has drawbacks. The remembered nicknames in Outlook get littered with the voicemail email addresses, that is Outlook remembers both and The real trouble is that VMO is not "really" on Outlook plugin, since it goes back to UC for everything. For example, there are still issues of being able to forward a voicemail email to someone else without the additional step of creating a new mail message and dragging the wave file over to it. If your UC users are LDAP (AD) integrated, their password is saved in VMO, so when they change their AD password, VMO will start locking their account because it is still has the old password. VMO does not work with shared mailboxes where View Mail with Unity 5 was just fine with them. Single Inbox is really "split personality" inbox, since UC retains a copy of all voicemails within UC. Another little landmine is that if your users do use VMO, they will never get a quota warning. Also UC can not do authenicated SMTP to its Smart Host. My photocopiers are smarter about email then UC is.

Yes I have given feedback on UC back to Cisco and I do hope they improve the product in the future. But hopefully this will help other people doing migrations to go in knowing where more of the pitfalls are.

I belevie I am running into a related issue, but not the same as you described. My single inbox works fine, we have a relay domain setup, voice messages can be replied to and arrive at the proper location. We do not experience any issues or problems with it comes to voice message delviery and routing.

We do however see multiple NDR for messages coming to/from either root@SERVERHOSTNAME or postmaster@SERVERHOSTNAME from both servers. As you see there is no .com or proper e-mail address is jsut root@SERVERHOSTNAME....

I posted about this specifically here:

With an example of one of the NDRs.....has anyone come across this? Or been able to resolve this? Please take a glance and help if you have some time. Thank you.


I Hope this could help :


Resolving SMTP Domain Name Configuration Issues 8.5 and Later

When a single inbox user receives a voice message, it is synchronized from Cisco Unity Connection to Microsoft Exchange. The email address of sender/recipient has Connection domain name, for example, userid@CUC-hostname . Due to this, email clients like Microsoft Outlook or IBM Lotus Notes adds the Cisco Unity Connection address as "recent contacts" in the address book. When a user replies to an email or adds recipient while composing an email, the user can enter/select the Cisco Unity Connection address, which may lead to NDR. In case you desire when the voice message is synchronized for single inbox users from Connection to Exchange, the email address of sender/recipient is displayed as the corporate email address, for example, userid@corp-hostname, you must perform the following steps:

Step 1

In Cisco Unity Connection Administration, expand System Settings > SMTP Configuration, then select Smart Host.

Step 2

On the Smart Host page, in the Smart Host field, enter the IP address or fully qualified domain name of the SMTP smart host server. (Enter the fully qualified domain name of the server only if DNS is configured).


Microsoft Exchange server can be used as a smart host.

Step 3

Click on Save.

Step 4

Configure SMTP Proxy addresses for users(For example, userid@corp-hostname). For more information see the "SMTP Proxy Addresses in Cisco Unity Connection 8.x" section in the Setting Up Features and Functionality That Are Controlled by User Account Settings in Cisco Unity Connection 8.x chapter of User Moves, Adds, and Changes Guide for Cisco Unity Connection.

Step 5

In Cisco Unity Connection Administration, expand System Settings, then select General Configuration.

Step 6

On the General Configuration page, in the When a recipient cannot be found list, select Relay message to smart host so that if the Recipient is not found, the message will be sent to the smart host.

Step 7

Click on Save.

Step 8

In Cisco Unity Connection Administration, expand Users > Edit > Message Actions. Select the Accept the message option from the Voicemail drop- down list. Make sure to select the Relay the message option from the Email, Fax, and receipt drop -down lists.

Step 9

Setup a recipient policy such that the Cisco Unity Connection alias resolves to the corporate email Id.

For Exchange 2010, see the following link: Unified Messaging Guide for Cisco Unity Connection for Release 8.5 Chapter 2 Configuring Cisco Unity Connection 8.5 and Later and Microsoft Exchange for Unified Messaging Testing Access to Exchange Calendars for Cisco Unity Connection 8.5 and Later

For Exchange 2003, see the following link:

For Exchange 2007, see the following link:

Step 10

On Exchange 2010 server, make sure to configure the secondary SMTP Proxy addresses for each server in Cisco Unity Connection clusters.(For example, userid@corp-hostname , userid@ CUC-hostname-publisher, userid@CUC-hostname-subscriber). Each Connection cluster has its own unique domain name.

Tray Stoutmeyer
Cisco Employee

I just added a link documenting the recommendation NOT to use your corporate domain as your CUC SMTP domain.

- Tray

UC Support

Hi team,

Can you please tell me how to reply using VMO? because VMO is integrated in outlook, when I hit reply, I get only outlook reply interface.


Tim Schroeder

Has anything changed in regards to this issue in the last 3 years?  It's now 2014 and I'm using Unity Connection 10.0 with Office 365 and having the same problem.  Is there a fix/workaround, or is setting up "Internal Relay Domains" in Exchange still the only solution?


Tim - what did you find out with Office 365 integration?


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