Outlook
2007 continues to support Cached Exchange mode. Cached Exchange mode,
or Cached mode for short, refers to a configuration where Outlook is
storing the messages and calendar items locally. Unlike the old Personal
folder file (PST) storage method, Cached mode utilizes an OST file.
This file is synchronized with the Exchange server on a regular basis.
This means that there are two copies of the mailbox at all times. One
copy lives on the Exchange server and one copy lives on the Outlook
client.
This configuration
has many advantages in terms of performance and reliability. For
example, imagine that a user is connecting to their Exchange server over
a dial-up connection and isn’t running Cached mode. The user receives a
message with a large attachment. The user sees the new message and
opens the attachment. Now, the message has to be downloaded to the
user’s computer. This takes several minutes because of the size of the
file and the relatively slow link speed. This usually results in unhappy
users because they had to wait several minutes between wanting to open
the attachment and the attachment actually opening.
Now, let’s view this
same scenario with Cached mode. In Cached mode, the attachment is
downloaded in the background when the message arrives, assuming the
Outlook client is attached to the server. The message with the
attachment doesn’t appear in the mailbox until
the contents have been downloaded and cached locally. Now, when the
user sees the message appear in the Inbox, the files associated with the
attachment are already on the local system. The user opens the
attachment and it opens immediately. This results in a happier user.
The truth of the matter
is that the download time of the message was exactly the same in both
scenarios. However, the perceived difference is that the Cached mode
situation was faster because the user doesn’t know when the message was
sent. This situation also takes great advantage of the idle time of the
user. Most messages arrive and are fully downloaded to the client while
the user is away from their system or doing other things. This means
that when the user is actively working with email, there aren’t any
delays in moving data.
Because the data downloaded
is only a mirror of the Exchange Server mailbox, the content available
via OWA is exactly the same. Similarly, if the user were to get another
computer or a new computer, Outlook simply creates another copy of the
data locally to keep in sync.
With the OST file locally
stored, the user is able to work with the contents of their mailbox even
when not connected to the Exchange server. Changes made locally will
sync back to the Exchange server. Like most replication performed by
Microsoft, the newest copy always wins and overwrites older changes.
This allows a traveling user to reply to messages, organize folders, and
create calendar entries while away from the office. Upon connecting to
the Exchange server, their local changes get applied to the Exchange
server copy. This is really an optimal configuration for traveling users
and users who have limited connectivity.
The User Experience in Cached Exchange Mode
When the user is
connected to the Exchange server, the phrase “Connected to Microsoft
Exchange” appears in the lower-right corner of the Outlook 2007 window.
The message “All Folders Are Up to Date” should also be displayed when
synchronization is up to date.
When connectivity is lost, the message says “Disconnected” and gives the date and time the offline folders were last updated.
When connectivity is
first restored, the message says “Trying to Connect.” As connectivity is
reestablished, the phrase “Connected to Microsoft Exchange” reappears,
and to the left are updates informing the user what is automatically
occurring to get the mailbox up to date.
These messages could be any of the following:
The user might
occasionally find that people appear to be missing from the Global
Address List (GAL). While running in Cached mode, Outlook 2007 no longer
gets its GAL from the global catalog. The client downloads the Offline
Address Book. This is what allows
the user to look up addresses while not connected to the network. The
user can trigger a download of the OAB at any time. Important to realize
is that, by default, Exchange Server only updates the OAB every 24
hours. As such, it’s possible for a user to be added to Exchange Server
after the OAB generation has occurred. Users not running in Cached mode
would see the new user in the GAL but the Cached mode users wouldn’t see
them until the OAB was updated and they downloaded the latest copy.
Deploying Cached Exchange Mode
Cached mode can be
deployed by using the Office Customization Tool or through enabling this
option using domain Group Policy. Be aware that setting it via Group
Policy on a large number of users drastically increases network traffic
to the Exchange server. Outlook in Cached mode has to download the
entire mailbox. Environments where mailbox size limits aren’t set are
especially impacted by this. Imagine 200 users logon on Monday morning
and a GPO sets their Outlook to Cached mode. If each user had 100MB of
mail in their mailbox, there would be 20GB of data being copied from the
Exchange server. This could be especially impacting if some of those
users were coming across WAN connections to get to Exchange Server.
If possible, only set a
user to Cached mode when they are on the same LAN of the Exchange server
or when they are first created in Exchange Server. This reduces the
traffic at the Exchange server.
Deploying Cached Exchange Mode Manually
When configuring a user’s Outlook profile manually, it’s possible to configure Cached mode at that time.
To configure Cached mode manually, do the following:
1. | Begin configuring a user profile in the standard manner.
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2. | When the E-Mail Accounts page is reached, make sure the Use Cached Exchange Mode check box is checked.
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3. | Finish configuring the Outlook profile.
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Deployment Considerations for Cached Exchange Mode
Because enabling
Cached mode forces the end users to synchronize a full copy of their
mailbox to a local OST file as well as a full copy of the OAB, the
demand on an Exchange server can be quite high. If a large number of
users must be configured to use Cached mode at one time, the best
choices for configuring Cached mode are as follows:
- Only
enable Cached mode if the user will benefit from it. This would include
traveling users or users who are on slow connections.
- Deploy Cached mode to groups of users at a time rather than to the whole enterprise.
- Encourage
users to clean up their mailboxes prior to enabling Cached mode. Sent
and Deleted items often account for 50% of the size of a mailbox.
- Deploy
Cached mode sooner rather than later. The smaller the mailbox at the
time of the OST creation, the less data needs to be moved.
Using Cached Exchange Mode
Because
Cached mode acts somewhat differently from a traditional mailbox, an
administrator might consider some additional user training for those
with Cached mode. This helps users recognize those differences and
should result in fewer calls to the help desk. Some of these differences
are mentioned in the following sections.
The Send/Receive Button
For users in Cached
mode, it is unnecessary to click the Send/Receive messages button
regularly when synchronizing with the new Cached mode functionality.
This now happens automatically and clicking Send/Receive doesn’t
accomplish anything.
RPC Over HTTPS and the Cached Exchange Mode
It is recommended that
users running RPC over HTTPS also run with Cached Exchange mode
enabled. This is because Cached Exchange mode deals better with “slow
links and disconnections” to Exchange Server. Because RPC over HTTPS
accesses Exchange Server information via the Internet, these users are
more likely to experience network latency and slowness.
Slow-Link Connection Awareness
Cached mode
was originally designed to address the challenges associated with links
128Kbps or slower. When slow-link connection awareness is enabled, it
automatically implements the following email-synchronization behaviors:
OAB is not downloaded (neither partial nor full download).
Mail headers only are downloaded.
The rest of the mail message and attachments are downloaded when the user clicks on the message or attachment to open it.
To change the slow-link configuration, perform the following steps:
1. | Click File.
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2. | Choose Cached Exchange Mode.
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3. | Uncheck On Slow Connections Download Only Headers.
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Cached Exchange Mode and OSTs and OABs
Using Cached mode
downloads a full copy of the user’s mail to the OST file stored locally
on the user’s hard drive. However, administrators need to be aware of
some considerations regarding OSTs and Cached mode to plan and make
their configuration choices for these Exchange Server clients allowing
optimal performance and efficient connectivity.
Cached Exchange Mode OST Considerations
OST files in Outlook
2007 use the new Unicode format. This allows them to go beyond the 2-GB
limitation of the old American National Standards Institute (ANSI)
format. However, be sure to account for the potential size of the OST
file when planning your desktop
or laptop images. Older notebooks might not have enough space locally
to support a large OST file if you aren’t limiting the size of mailboxes
on the Exchange server.
Cached Exchange Mode and Outlook Address Book (OAB) Implications
When using Cached
mode, it is possible to download a No Details Outlook address book.
However, users in Cached mode should download the Full Details OAB. This
is because they can experience significant delays when they access the
OAB when the full details are not locally accessible. When this
situation occurs, the user’s workstation must contact the Exchange
server to provide full data for the OAB. This results in delays for the
user during the download.
When Cached
mode is enabled, the OAB is synchronized every 24 hours, by default. If
there are no updates to the server OAB, there will be no updates to the
offline OAB. When there are changes to the OAB, only the differences are
downloaded. This results in a faster update to the OAB for the Cached
mode user.
Outlook Features That Decrease Cached Exchange Mode’s Effectiveness
Cached Exchange
mode is easy to configure and provides many benefits to the occasionally
offline user. It is important to try to keep the Cached mode experience
as positive as possible for the user. Thus, it is useful to know that
several Outlook 2007 features can actually decrease the effectiveness of
Cached mode. The features discussed in the following sections all
result in Outlook 2007 sending calls to the Exchange server for
information when in Cached mode. For users using Cached mode, these
calls can greatly decrease the effectiveness and performance of the
client and, therefore, should be avoided if possible.
Delegate Access and Accessing Shared Folders or Calendars
These two items both
require access to the Exchange server to view other users’ Outlook
items. Cached mode does not download another user’s data to the local
OST, so this nullifies the use of Cached mode when the functionality is
required. These functions will work while the Cached mode user is
connected to the Exchange server, but it can result in attempted
external connections that will fail when the user is offline. This
results in the interface waiting for a timeout before continuing with
its processes.
Outlook Add-ins
Outlook add-ins
such as ActiveSync can result in Outlook not utilizing important items,
such as the Download Headers Only functionality that allows Cached mode
to work so well. They also can cause excessive calls to the Exchange
server or network. Avoid Outlook add-ins, if possible. Third-party
add-ins should be tested with Cached mode for both online and offline
behaviors to see if they are making calls to nonlocal data that could
impact Cached mode users while they are offline.
Digital Signatures
Verification of
digital signatures requires Outlook to verify a valid signature for
messages sent using digital encryption, requiring a server call as well.
Be sure to test such configurations to ensure that signed or protected
content can still be accessed while a user is offline.
Noncached Public Folders
This, too, requires
bandwidth and a call to the server. Consider synchronizing frequently
used public folders to the OST through the use of Public Folder
Favorites. Be careful not to cache too much public folder information
because it inflates the size of the OST file.
Including Additional Searchable Address Books
If the enterprise
includes custom address books and contact lists that are enabled to be
searchable and usable for email addressing, this results in the
client/server communications. These types of address lists are not
cached by Outlook.
Customizing the User Object Properties
If the enterprise has
created customized items on the General tab of the properties box of a
user, this always requires a call to the server: When user properties
are displayed, the General tab is always displayed first. Therefore, if
these are necessary, consider placing any customized fields on a
different tab on the user properties pages requiring a call to the
server only when that tab is accessed, not every time the user
properties are accessed.
