Is your Outlook client downloading an ANSI or Unicode OAB?

A Microsoft Exchange server can contain 3 different version of the OAB (OAB Version 2, OAB Version 3 and OAB Version 4). As newer versions of the Offline Address Book are created and rolled out through an organization, it can become difficult for administrators to keep track of which version of the OAB users are downloading. This blog will hopefully help to clear this up a bit.

A Microsoft Outlook client can download the OAB Version 4 only if the following criteria have been met:

  • The Microsoft Exchange 2003 Server has had Service Pack 2 applied
  • The OAB Version 4 has been enabled
  • The Microsoft Outlook client has had Office Service Pack 2 installed

For Exchange 2007

  • OAB Version 4 is being generated.
  • The OAB Version 4 needs to be replicated to a Web Distribution Point
  • If public folders are enabled, the OAB Version 4 needs to be posted
  • The user is running Microsoft Outlook 2007
  • The user is running Microsoft Outlook 2003 with Office Service Pack 2

This download will occur when an OAB update is required, for example this can occur due to the 24 hr update frequency or if the user manually attempts an incremental or full OAB download.

The location in the registry that contains the Microsoft Outlook provider settings is:  HKEY_CURRENT_USER\Software\Microsoft\Exchange\Exchange Provider.

The following registry values will reside under this registry key (These can change based on Outlook client version):

"MOABU"                                  = eb6bc4ba-2128-4380-96d1-4fd912a0ba43
"OAB DNU"                               = The Unicode DN
"OAB Last Modified Time"           = Last Modified Time
"OAB Last Template LocaleU"     = Last OAB Template Locale Version
"OAB Last Template UI LocaleU" = Last OAB Template Locale UI
"OAB NameU"                            = Global Address List
"OAB SeqU"                               = OAB Sequence Number
"OAB Sort LocaleU"                    = OAB Sort Locale               
"OAB Use UTF8"                        = 0 or 1

Note on MOABU - If the registry key is MOAB, the Exchange server is using an ANSI Offline Address Book. If the registry key is MOABU the Exchange server is using a Unicode Offline Address Book.

Note on "OAB Sort LocaleU" - The OAB can only use the sort locale and character set of the server where it is generated. For example, if you have an Outlook client that is Spanish connecting to an Exchange server, you can add the Spanish locale to the Exchange server. However, the primary locale is going to be whatever was installed; let's say English. When the OAB is generated, it will use the English locale.

Note on “OAB Use UTF8” - This value will be set to 1 if the client was able to download the Unicode Offline Address Book and to 0 for ANSI Offline Address Book. 

Note on "OAB SeqU" - This is the sequence number for the OAB files that have been downloaded. For example, (Example - 0a 00 00 00 = 10)

Registry Locations
The following location in the registry will contain the settings for the Microsoft Outlook profiles:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles.

The following location will contain the profile specific settings: HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles\Outlook\13dbb0c8aa05101a9bb000aa002fc45a

How to configure your Outlook clients for only OAB Version 4 downloads
Now if an administrator wants to ensure that the users in an organization are *only* able to download the OAB Version 4, they can implement this two ways:

1. Manually set the registry key on each client (not a very efficient way).
2. Push out a policy through a GPO (Group Policy Object) in the Active Directory.

You will want to navigate to the following location in the registry: HKEY_CURRENT_USER\Software\Policies\Microsoft\Exchange\Exchange Provider and add the following value:

Registry Name = "OAB v4 Only"
Registry Type = DWORD
Registry Data = 0 or 1

0 - Is the default setting if the registry key is not set, not present or set to something other than this on the client. If this is the case the Microsoft Outlook will perform the same fall back logic as it does today.

Example - If OAB Version 4 is unavailable for download the Outlook client will try to download OAB Version 3 and so on.

1 - Outlook will only use OAB v4, regardless of what other OAB versions are present on the server. If no OAB Version 4's are available for download or this registry value is set, the Microsoft Outlook client will not use an OAB and will use the Online Global Address List instead.


  1. This registry key is not applicable to ANSI mode profiles, which are limited and can only use OAB Version 2.

  2. If you have an ANSI profile you will need to create a new profile as ANSI profiles can not be automatically upgraded to Unicode profiles.

For more information on how to tell which version of the OAB a Microsoft Outlook client is downloading, please see: Troubleshooting Offline Address Book Downloads with Outlook Diagnostic Logging (Event ID 27) -

So just as a recap. If you are are interested in finding out what version of the OAB your client it downloading, you need to check for the following:

  1. "OAB Use UTF8" registry key and make sure it is set to 1. This will indicate that you are downloading a Unicode profile. Now even know this can be OAB Version 3 or OAB Version 4 you can still verify this.
  2. Turn up advanced logging from with-in Outlook and look for the Event ID 27 in the Windows Application Log.
  3. Follow blog
  4. Add the "OAB v4 Only" registry key via Group Policy Object.


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  1. Another problem I have seen in the newsgroups and floating around on the internet is that people are…

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