Exchange Special Mailboxes Part 3 – SMTP mailbox

This post is the third post in a series. Special thanks to Scott Landry for his additions to this post.
You may also be interested in the earlier SystemMailbox and System Attendant mailbox posts.


SMTP (servername-{guid}) mailbox

What is it and what is it used for?


SMTP (servername-{guid}) mailbox is used by the mail transport of Exchange 200x as a temporary holding place for various messages as they pass through the system.


Inside the SMTP mailbox you can find the following folder structure:


SMTP Mailbox folder hierarchy


The folders MTS-IN and MTS-OUT are fairly well documented in the Exchange 2003 SDK Message Transfer documentation. They are used by EDK connectors to facilitate the transfer of messages between the MTA and the Store. They are also used for X400 Connectors, Site Connectors, Fax Connectors… pretty much anything that uses the MTA.


So then, what about these TempTable folders? When a message is processed by Exchange transport, the message remains in one place while passing through the various phases and memory based queues. If the message originates from the SMTP protocol (another Exchange 200x server or the Internet), then as the message comes in, it is written via the NTFS store driver to the mailroot/queue folder while going through categorization & advanced queuing.  If the message originates from any where else -- MAPI client, OWA, or the MTA, then the message remains in the store during the same process, in the SMTP mailbox accessible to transport via the Exchange store driver using IFS.  No matter where the physical message resides during transport processing, the queue viewer in ESM will show messages from both places.


Where can it be found?


An SMTP mailbox will be created on each Mailbox Store. It’s stamped with the servername and the mailbox store GUID, so it should be fairly easy to identify. There is a mailbox object within the mailbox store, and a corresponding SMTP mailbox directory object in the Active Directory. The directory objects are found under the CN=Connections,CN=<orgname>,CN=Microsoft Exchange,CN=Services,CN=Configuration,CN=<domain> container.


When does it get created?


The SMTP mailbox is created in a mailbox store when the store is first created and mounted.


Should I delete it? Do I have to delete it before I can uninstall the Exchange server?


Nope, definitely should not delete it. If you’re getting the error “One or more users currently use this mailbox store. These users must be moved to a different mailbox store or be mail disabled before deleting this store. ID no: c1034a7f Exchange System Manager” when trying to remove the mailbox store or uninstall the server, this is not due to the SMTP Mailbox. Have a look at KB.279202 for more information on how to determine which mailbox is causing this behaviour.


Can it be moved and/or how do I recreate it?


It wouldn’t make much sense to move the SMTP mailbox, since it’s so tightly associated with the server name and GUID of a particular mailbox store.


If the SMTP mailbox is somehow deleted from a mailbox store, but the directory object remains, it’s as simple as dismounting and remounting the mailbox store. If the directory object is in place and is valid, the store will automatically recreate the SMTP mailbox object within the mailbox store. If it doesn’t you may need to have a look at KB.828938 for additional options.


If the SMTP mailbox directory object does not exist, the SMTP mailbox object in the mailbox store will become disconnected and will not be functional. You will see events 1022, 326, and 1194 logged in the application log. Generally if this happens, mail will just sit in the outbox. You’ll need to recreate the SMTP mailbox following the steps in KB.828938. Alternately (and a bit easier), create a new mailbox store and move users from the store without an SMTP mailbox over to the newly created mailbox store.


How can I log onto the SMTP mailbox?


This is possible, but you’re best to only do it under the advisement of PSS. There is a tool called Profinst which will create a MAPI profile to the SMTP mailbox. Note that there are several versions of this tool and if you run the wrong version (for instance, running the Exchange 5.5 version against an Exchange 2000 or 2003 server) it can cause problems. For Exchange 200x, you want the version dated 8–21–2001 (or newer), which should be about 28kb which can be found at:


Updated Jan 25,2005: As another method, have a look at MFCMAPI ( MFCMAPI can be used to logon to the SMTP mailbox without creating an explicit profile with Profinst. Just fire it up, logon with whatever profile you want, then select “Get Mailbox Table” from the MDB menu. Finally, double-click on the mailbox you want to open up. Presuming you have proper rights, you’re right in!


What happens if I don’t have a proper SMTP mailbox?


If your SMTP mailbox is non functional, mail will not be able to pass through local delivery into the store or exit the store outbound for SMTP or EDK connectors. This will manifest as mail queuing up inbound to the store and as mail sitting (forever) in the outbox within Outlook. Note that this is not the only thing that can cause mail to queue or to sit in the outbox, and particularly if the mail eventually goes through it’s likely not the problem… but it’s definitely something to check if mailflow just stops. 

Comments (5)

  1. Anonymous says:

    Jason Nelson goes into a bunch of more and better detail on the specific Exoledb-related folders in the…

  2. Anonymous says:

    Jason Nelson goes into a bunch of more and better detail on the specific Exoledb-related folders in the…

  3. Anonymous says:

    Evan Dodds posted a great series on Exchange special mailboxes on his blog. There were 3 parts in that…

  4. Thanks for the clarification Evan! Your blog is definitely my favorite one! I encourage all my students to visit the exchange team blog and especially your blog… 🙂

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