If you are having problems with your email, one common diagnostic aid is a complete list of the message's headers. Headers show the path a message took to get from the sender to the recipient. The IT Service Desk or other technical support may ask you to provide a message's headers.

In Add New Account window, a username is highlighted by the underline that implies that your profile has been set up. After that, click on NextFinish. Users are now aware of the configuration method of Office 365 with Outlook 2016, 2013, 2010, 2007. The user is running Outlook 2016 with the latest 32bit build (19.0.9330.2073) as part of their active Office 365 Personal subscription, with an Outlook.com E-Mail address set up in Outlook. The Focused Inbox button is missing under the View tab, and adding it manually on the quick access toolbar results in a button that is greyed out.

Right-click (or ctrl-click) the message in your Inbox or other folder (do not open the message).
From the menu that appears, select View Source.

Your text editor (typically an application called TextEdit) will open, displaying all the headers for the message, followed by the message body.

If you need to copy the headers (to paste somewhere else),

Drag over the text from the beginning of the text to the beginning of the body of the message.
Press command-c on your keyboard; this copies the highlighted text to the clipboard.
Then, with an email message or other document open, press command-v to paste the header text into that document.

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Outlook 2016 provides two basic connectivity modes when you are connected to Exchange Server: Cached Exchange Mode and Online Mode.

Note

This article is for IT Pros and admins that are deploying and configuring Outlook 2016 for Windows for users in their enterprises. If you're a user trying to configure your Outlook settings, see Turn on Cached Exchange Mode.

Comparison of Cached Exchange Mode and Online Mode

Cached Exchange Mode gives users a seamless online and offline Outlook experience by caching the user's mailbox and the Offline Address Book (OAB) locally. With Cached Exchange Mode, which is the default setting for users, Outlook no longer depends on continuous network connectivity for access to user information. When a user is connected, Outlook continuously updates users' mailboxes so that the mailboxes are kept up to date. If a user disconnects from the network, for example, by moving to an area without Wi-Fi access, the user can continue to access the last available email data.

Important

We recommend always using Cached Exchange Mode with an Office 365 account.

Online Mode works by using information directly from the server, and, as the name implies, it requires a connection. Mailbox data is only cached in memory and never written to disk.

Cached Exchange Mode is the preferred configuration in Outlook 2016 and is useful in the following situations:

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Users who frequently move in and out of connectivity.
Users who frequently work offline or without connectivity.
Users who have high-latency connections (greater than 500 ms) to Exchange Server.

Online mode is useful in the following situations:

Kiosk scenarios, where a particular computer has many users who access different Outlook accounts—and the delay to download email messages to a local cache is unacceptable.
Heavily regulated compliance or secure environments where it is a risk to store data locally. In addition, we recommend that you consider using Encrypting File System (EFS) or BitLocker as a robust solution.
Large mailboxes on computers that don't have sufficient hard disk space for a local copy of the mailbox.

Even when it is configured in Cached Exchange Mode, Outlook 2016 must contact the server directly to do certain operations. These operations won't function when Outlook is not connected and can take longer to complete on high-latency connections. These operations include the following:

Working with Shared Folders that were not made available offline.
Retrieving Free/Busy information.
Setting, changing, or canceling an Out of Office message.
Accessing public folders that were not made available offline.
Retrieving rights to a rights-protected message.
Editing rules.
Retrieving MailTips.
Retrieving Policy Tips.

Delayed delivery options are client side in cached mode and server side in online mode. So, when you use Cached Exchange Mode, Outlook must be connected and open at the assigned delivery time for the delayed delivery message to be sent.

Outlook 2016 supports running in Cached Exchange Mode in a Remote Desktop Services (RDS), formerly known as Terminal Services, environment that has multiple users. When you configure a computer running RDS to use Cached Exchange Mode, be sure to consider the additional storage space and disk I/O that are required for multiple client accesses. New Exchange accounts set up on computers running RDS use Online Mode by default. At setup, the user can decide to enable Cached Exchange Mode.

Planning considerations for Cached Exchange Mode for Outlook 2016

In some cases, you can improve the performance of Cached Exchange Mode for your whole organization or for a group of users—for example, users who work remotely.

Outlook data file (.ost) recommendations

When you use Cached Exchange Mode, be aware that users' local .ost files are 50 percent to 80 percent larger than the mailbox size reported in Exchange Server. The format that Outlook uses to store data locally for Cached Exchange Mode is less space-efficient than the server data file format.

The maximum size for .ost files are configurable. The default is 50 GB of data storage. Make sure that users' .ost files are located in a folder that has sufficient disk space to accommodate users' mailboxes.

For more information about how to deploy .ost files to a location other than the default location, see To configure a default .ost location by using Group Policy
For more information about how to configure .ost file size, see How to configure the size limit for both (.pst) and (.ost) files in Outlook.

Upgrading existing Cached Exchange Mode users to Outlook 2016

When upgrading, if you do not change Cached Exchange Mode settings, the same settings are kept for Outlook 2016.

However, by default, when Outlook 2016 is installed and Cached Exchange Mode is enabled, a new compressed version of the Outlook data file (.ost) is created. The earlier version of the .ost file is kept and, if it is necessary, can be opened by Outlook 2016. If you must keep Outlook 2016 from creating a new compressed Outlook data file (.ost), use the Group Policy template for Outlook (Outlk16.admx) to enable the Do not create new OST file on upgrade policy setting.

For more information about how to configure this and other settings, see Using Group Policy and the Office Customization Tool (OCT).

Note

The Exchange Fast Access feature that was added to Outlook 2013 Exchange Cached Mode has been deprecated in Outlook 2016.

Managing performance issues in Outlook

Most users find that Cached Exchange Mode performs faster than online mode. However, several factors can influence a user's perception of Cached Exchange Mode performance, like hard disk size and speed, CPU speed, .ost file size, and the expected level of performance.

For troubleshooting tips about diagnosing and addressing performance issues in Outlook, see How to troubleshoot performance issues in Outlook.

Managing Outlook folder sharing

By default, when Cached Exchange Mode is enabled, shared mail and nonmail folders that users access in other mailboxes are downloaded and cached in the user's local .ost file. Similarly, if a manager delegates access to his or her Inbox to a team member, when the team member accesses the folder, Outlook 2016 also starts caching the Inbox folder locally.

You can disable caching of all shared folders for profiles that have Cached Exchange Mode enabled. To do this, configure the Download shared non-mail folders option in the Office Customization Tool (OCT) when you customize your Cached Exchange Mode deployment. This setting applies to both mail and nonmail folders in Outlook 2016.

If you want to disable caching of shared mail folders (like a delegated Inbox) but not shared nonmail folders (like

Outlook 2016 For Mac Show Ruler