Exchange Global Address List and the Outlook Offline Address Book

Exchange Global Address List and the Outlook Offline Address Book



This document seeks to address and clarify the small misunderstanding surrounding the GAL (Global Address List) and the OAB (Offline Address Book).

Quite often all Administrators, even Exchange Administrators simply refer to the users they see in the Address section of Outlook casually as the GAL for ease of reference, but really more often than not, you are looking at the OAB.

However sometimes in large complex organisations we have a situation where a new joiner joins and their colleagues want to email them immediately, but they don’t appear in Outlook for them so they call the Helpdesk “Why isn’t Joe Bloggs in the GAL??”

Well, the truth of the matter is that our new joiner Joe is in fact in the GAL, he just hasn’t yet made it to everyone’s Outlook Client – the Offline Address Book.

** This Blog is based on the assumption that all Outlook users are in cached mode.



After a change had been made to any attribute in f the Exchange / AD Address Book that are also included in the Offline Address Book (OAB), the following occurs:

1. Exchange regenerates the OAB

·       Default generation schedule: 24 hours

2. Exchange OAB Server distributes the OAB (Only for Exchange 2010, Exchange 2013 uses proxying instead)

·        Default distribution schedule: 480 minutes

3. Outlook downloads the OAB

·        Default update schedule: 24 hours

This means that in the worst possible scenario, an update to the Address Book won’t become available to the user until about 48 hours after the change.

This situation however is extremely rare since the default maintenance time on Exchange is at 5:00 AM and updates and downloads are usually performed during working hours.

Global Address List aka “The GAL”

*** NOTE: The GAL is essentially a real-time / online representation of AD Objects that are Mail Enabled for Microsoft Exchange ***

The GAL contains information for all email enabled users, Distribution Groups, and Shared Mailboxes and Exchange Resource Mailboxes.

GAL Objects are directly viewable in the Exchange Management Console/Shell and OWA and Microsoft Outlook BUT ONLY IN ONLINE MODEnot cached mode.

Exchange Attributes


The GAL will only present objects that have AD Attributes beginning with msEXCH* (and some others) populated that it uses to filter on.  If these attributes are present, then the AD Objects that are Mail-Enabled or Mailbox-Enabled will appear in the GAL – and ultimately the Offline Address Book.

You can see the list of attributes that will be put into the GAL using

Get-OfflineAddressBook 'Default Offline Address Book' | select -expandproperty configuredattributes

Some examples of these attributes includes:













The Offline Address Book


When Outlook users are running in cached mode, they rely on the Offline Address Book (OAB) to provide them with access to one or more addresses (that are always available when they are connected directly to Exchange)

The OAB is rebuilt and downloaded on a default schedule as shown below.  Because of this, a new user may not be visible in the address book, or changes to a user’s name, address, etc. may not be available even though such changes have been made in Active Directory. This can occur even though no errors are present within the OAB rebuild process.

Offline Address Book Generation


The OAB generation server creates the new OAB once per day at 5am


(* on the Server running it)

Offline Address Book Generation

The CAS servers poll for changes every 8 hours

As mentioned before, this is only for Exchange 2010, Exchange 2013 avoids this step through the use of proxying

CAS Polling


The Outlook client polls for changes every 24 hours


If left constantly running, Outlook in cached mode automatically updates the offline address book on the client every 24 hours.


The 24-hour time period is measured from the time that the offline address book was last downloaded successfully


For example, if you complete an offline address book download at 09:00 today, Outlook will start the offline address book download the next day at approximately 09:00. Therefore, different people will receive updates at different, random times.

The Offline Address book is downloaded by Outlook when it starts automatically. There is nothing else to change.


If you want to change the download interval, then that isn’t possible – Automatically Outlook will only download the OAB once every 24 hours or within 1-5 minutes when Outlook is restarted.



Q. How can a user update their Offline Address book immediately?

A. There are three ways:

1) Try a manual Re-Sync

Manual ReSync 1

Manual ReSync 2
2) Close Outlook and delete the *.OAB files manually From here:
C:\Users\%username%\AppData\Local\Microsoft\Outlook\Offline Address Books\*\*.*

Delete OAB files

3) Delete and Recreate their Outlook Profile

Delete Oulook Profile 1

Delete Oulook Profile 2

Start Outlook again and follow Prompts

Q:           If I cannot see a see if a user/group/shared mailbox in my Outlook OAB, how can I tell if it is present in the Global Address List?

A:            There are five ways.

  1. Look in the Outlook Web App (OWA). OWA looks directly to the GAL for email referencing

View GAL in OWA

  1. Look in Outlook non-cache mode

a.       In Cached mode Outlook always users the OAB to display users

View GAL non cache mode

Use OAB non-cache mode (whilst still using Cached Mailbox Mode)

Close Outlook

Go to your registry and find this branch:

HKEY_CURRENT_USER\Software\Policies\Microsoft\office\14.0\outlook\cached mode

Set the DownloadOAB key to 0 (ZERO)

View GAL RegKey OAB online


4)    Look directly in the Exchange Management Console

View GAL in EMC


Use The Exchange Management Shell

C:\Windows\system32>Get-Mailbox “Conrad Murray*” | FL

: {\Mailboxes(VLV), \All Mailboxes(VLV), \All Recipients(VLV), \All Users,
\Default Global Address List}

: False

: False

 ** You could also use Active Directory Users and Computers Attribute Viewer to look for the attributes listed above

View GAL in ADUC 1

View GAL in ADUC 2


Q. How can I see when Exchange last updated the OAB

Get-OfflineAddressBook|FL LastTouchedTime


LastTouchedTime GUI