SMTP Considerations for Unity Connection Single Inbox (i.e., Unified Messaging)


I think it is safe to assume that most of you know what the Single Inbox feature is all about.  However, Bill Bell once told me a little something about assumptions and he’s right a lot (except, of course, when he’s not).  Ok, so Single Inbox is a new feature introduced in Unity Connection 8.5, which provides Unified Messaging capabilities for customers that have Exchange 2003, 2007, and/or 2010.  Recently, I’ve looked at considerations for moving from good ol’ fashioned Unity Unified Messaging to Unity Connection with Single Inbox.  It’s important to note upfront that, while both provide the same feature (Unified Messaging), the method by which this is accomplished is quite different.  I’m not going to delve into that discussion here; however, you can refer to my CMUG presentation for more details here:

UC 8.x Applications Update

OK…so now that you’ve had ample time to review the CMUG presentation then let’s get on with it.  Aside from the obvious differences, I’ve also encountered some things that don’t appear to be laid out too clearly in existing documentation.  The first question generally is about the use of ViewMail for Outlook.  The main documented difference is that if you do not use ViewMail for Outlook then messages are simply treated as emails with .WAV attachments.  Given the proliferation of devices on which we can access data, there are inherently going to be questions about what that really means because it’s unlikely that 100% of your Single Inbox users will be using an Outlook client with ViewMail for Outlook installed at all times.  What this discussion translates into is a review of SMTP-related configuration points.  What I really want to see is more clarity in the documentation for Single Inbox that ties things together in a logical, cohesive manner.   For now, here is how I step through the scenario and look for things that may come into play:


When Bill Bell leaves me a voice message on Unity Connection that is synced with my Exchange via Single Inbox, that message will have a reply address of

NOTE:  The SMTP address/domain displayed is that of the Unity Connection server (, which is not the same as my corporate Exchange SMTP domain (  This is basic messaging…no surprises, here.  Unity Connection mailboxes are assigned to an SMTP domain which, by default, is the FQDN of the server (or the Publisher in a cluster).  You can also optionally change the SMTP domain for Unity Connection; however, you should not set it to be the same as the corporate Exchange SMTP domain (not a good idea).

SMTP Considerations

  • Configure Exchange to route mail destined for the Unity Connection SMTP domain to the Unity Connection server.

NOTE:  How you accommodate this within Exchange depends on which version you use. 

  • By default, Unity Connection does not accept SMTP connections.  Configure Unity Connection to accept SMTP connections.
  • Configure each Single Inbox user’s Message Relay actions to relay email messages to the user’s corporate (Exchange) email address.
  • Unity Connection needs to be configured with an SMTP Smart Host.  I get a lot of questions about what “Smart Host” means so, for the record, it simply means a server that is configured to perform SMTP relay.  In this case, my relay server could be my Exchange server (
  • The SMTP Smart Host (i.e., SMTP relay server) needs to be configured to accept relays from Unity Connection.  Likewise, the relay server needs to know how to route messages for various domains.

NOTE:  How you accommodate this within Exchange also depends on which version you use.  There are also some other considerations (such as security) that come into play here as well.  The bottom line is that the Smart Host has to be “smart” enough to relay messages from Unity Connection to Exchange.

8 responses to “SMTP Considerations for Unity Connection Single Inbox (i.e., Unified Messaging)

  1. Is this really "Unified Messaging" ? or is this simple "relay the voicemail to my email inbox"

    Unified Messaging would keep your exchange inbox sync’d with Unity Connection, not relayed over to exchange from Unity Connection. True unified messaging wouldnt have SMTP involved at all on Unity Connection, just using the microsoft exchange api.


  2. The syncing of your voice messages with Exchange is done via the Exchange API not via relay. To me, two keys to UM are 1) that voicemail ends up in the Inbox and 2) notification is synced. Both of these goals are accomplished here via the API’s. In the example, the message has already been synced into the Inbox.

    In the documentation for Single Inbox, there are 2 deployment scenarios. The first is to use ViewMail for Outlook. The second is to use Single Inbox without it. To clarify, I am only walking thru things one [i]may[/i] need to consider when deploying Single Inbox without ViewMail for Outlook based on documentation. Here is an example of what sparked my list of things to consider:

    I hope to update or follow-up at some point once I’ve had more time with the feature and various scenarios.

  3. but with your documentation, MWI is not synchronized. If the message action is set to accept and relay, the MWI will be on till you check VM via TUI.

    relay my give you a single inbox, but not true Unified Messaging.

  4. I’m sorry if this is unclear as it appears you may have misinterpreted the scenario. The MWI is synchronized. This is part of the Single Inbox feature and is accomplished via web services (WebDAV, EWS). In the scenario, as soon as the message is synced into Exchange – the MWI is turned ON. Once read, it will turn OFF. No issues.

    When you use ViewMail for Outlook then the documentation states that replies/forwards/etc can be synchronized using that application. The follow-on is thinking in the blog is on how an email reply would work WITHOUT ViewMail for Outlook. The relay action is optional – there are different action options for message types.

    So, to be clear – relay is not required for Single Inbox to work. MWI is synced via the integration that enables the feature.

  5. Hello David, how can I synchronize mwi notification and email notificacion? Can the lamp of the phone be turned off if I play the .wav file in my email?

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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.


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