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Mark E. Smith's Brain Dump > Posts > Outlook's Ambiguous Name Resolution (ANR)
October 16
Outlook's Ambiguous Name Resolution (ANR)

How Outlook resolves names
There are three ways that Outlook will resolve names to email addresses. The online Global Address List (GAL), the Offline Address Book (OAB), and the Outlook Nickname Cache (commonly known as the Outlook type-ahead/auto-complete feature).

·         Nickname Cache (auto-complete): The nickname cache is dynamically built as the user sends email. Names are cached on the client side as messages are sent and “auto-complete” is populated.

·         Online GAL: When the online GAL is used a query is made directly to the Active Directory servers. Running in online mode not only adds addition traffic when sending email, adding names to the recipients list, and other name resolution tasks outlook performs. It adds additional network traffic and load to the domain controllers because Outlook makes constant LDAP queries to the Active Directory server to resolve name.

·         Offline Address Book (OAB):  Depending on the organization’s configuration of Outlook’s Send/Receive group frequency, Outlook 2003/2007 will download a local copy of the Online GAL called the Offline Address List. When users are offline or running in cached mode, unknown names will be resolved when Outlook makes queries to this offline address book then saves the name in the Nickname Cache for future use.

The issue
When running in cached mode, the default Outlook configuration only uses the Offline Address Book for unknown name resolution. When resolving and verifying names and email addresses, the OAB checks on fewer properties of a user/contact  than the GAL. This results in a more limited name resolution. The following table lists the properties available from the OAB and those available by default from the online GAL.

Fields available for name resolution

Active Directory Property

Description

Available in OAB

Available in online GAL

displayName

Display name

X

X

mail

SMTP address

 

X

givenName

First name

 

X

legacyExchangeDN

Distinguished name for backward compatibility with older Exchange systems

 

X

mailNickname

Exchange alias name

X

X

physicalDeliveryOfficeName

Office

X

X

proxyAddresses

All email addresses for the user

 

X

name

LDAP common name

 

X

sAMAccountName

Windows NT 4.0 logon name

 

X

sn

Surname

X

X


Examples of Name Resolution with the Offline Address List and First Last display name (default configuration)

User Types in “To” Field

Found in OAB?

Why

Mark Smith

Yes

Display name is “Mark E. Smith” so exact match is not found. Outlook finds all Mark Smith(s)

Mark

Yes

All display names with Mark will be displayed

Smith

Yes

All display and last names with Smith will be displayed

Smith, Mark E.

Yes

Last name is searchable in OAB

Mark E. Smith

Yes

Exact match on Display Name Field

 

Result: All name combinations are easily searchable in the OAB when First Last display names are used.

Examples of name resolution with the Offline Address List when Display Name is we switched to Last, First:

User Types in “To” Field

Found in OAB?

Why

Mark Smith

No

Mark Smith does not match any fields searchable in the OAB.

Mark

No

First name field is not searchable, does not match beginning string of display name field. Last names starting with Mark will be returned.

Smith

Yes

Last name is searchable and matches beginning string of display name field

Smith, Mark E.

Yes

Matches Display Name

Mark E. Smith

No

Mark E. Smith does not match any fields searchable in the OAB.

Smith, Mark

Yes

Exact match on Display Name Field

  

Solution:
Force Outlook Name Resolution queries to use the Online Address Book. This is done by changing the registry key on each workstation running Microsoft Outlook:

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Cached Mode\[ANR Include Online GAL] = 1

NOTE: Online GAL queries will not work when users are offline (disconnected from the network – in flight, etc) and will fall back to using the Offline Address Book.

See article Q821124, “How to force Outlook 2007 or Outlook 2003 to resolve proxy addresses and custom properties in Cached Exchange Mode” in the Microsoft Knowledge Base at http://support.microsoft.com.

Importance of Reviewing Outlook ANR Setting

ANR (Ambiguous Name Resolution) is the ability of Outlook or other LDAP clients to determine information based on partial data.

When using Outlook, a user might enter partial data in the From, To, CC or Bcc fields. The client, with the help of Active Directory will try to match the partial data and provide the address of the matching object. If an exact match is found then the address representing the matching object will be auto completed. If an ambiguous match is found then all potential matches are displayed and the client is allowed to choose the object he or she want to use.

If Outlook clients have ANR enabled this will result in additional network traffic and load on the domain controllers in the form of LDAP queries.

UPDATE:

OAB v4 did include changes to what properties are indexed. I will attempt to update this blog entry .to reflect those changes as time permits.

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