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 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.
1. 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 only updates the OAB every 24
hours. As such, it’s possible for a user to be added to Exchange 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.
2. 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 log on 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.
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. 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 then later. The smaller the mailbox at the
time of the OST creation, the less data needs to be moved.
3. 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 Cached Exchange mode enabled. This is because Exchange
Cached mode deals better with “slow links and disconnections” to
Exchange. Because RPC over HTTPS accesses Exchange 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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4. 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 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.
5. 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.
