Outlook 2013 added a new feature, Sync Slider, that limits the amount of mail synced with Outlook, in an effort to limit the size of the offline cache file used by Exchange or IMAP mailboxes.
In Outlook 2013, only the account mailbox is affected by the sync slider, the setting does not apply to shared or delegated mailboxes. In Outlook 2016, the sync slider also limits the age of mail sync in shared mailboxes that are cached.
For Outlook 2013, Exchange accounts can sync as little as 1 month, while Outlook 2016 can sync as little as 3 days of messages.
To view mail that is not synced down, click on "Click here to view more on Microsoft Exchange" at the bottom of the message list.
In Outlook 2016, shared mailboxes do not (currently) have the link (or active View on Server button) to view more messages on the server. Users will need to use Instant Search or OWA to view older messages.
The sync settings do not apply to the following Outlook items. These folder types are synced in full.
- Shared or delegated (Outlook 2013 only)
Shared or Delegate Mailboxes
When Exchange server users have shared or delegate folders, shared mailboxes, and public folders in a profile, Outlook 2013 caches the contents of these folders in the *.ost file, however, the sync setting does not apply to these folders, and all contents of these folders are stored in the local cache file.
Outlook 2016 applies the sync setting to shared or delegate folders and mailboxes, and public folders that are cached. It does not apply the sync settings to the new Groups feature as Groups are cached in in a separate data file (account-name.nst).
Users who need to limit the amount of data cached locally can set up filters on each folder. To do this, right click on the folder and choose Properties, Synchronization tab. Click the Filter button and create a filter. You'll need to repeat this on each folder where you want to limit what syncs.
Because only Public Folder Favorites sync, removing folders not needed offline from the Public Folder Favorites list will help to reduce the size of the cache. You can also disable caching Public Folder Favorites or Shared folders in Account Settings > More Settings.
Note that the non-mail folders and the Outbox are exempt from Sync Slider setting.
Change "Mail to keep offline" Setting for all Users
From our EMO mailbag: administrator had a question about the Sync Slider setting in Outlook 2013. This is the slider in Account Settings that lets you keep a few weeks or months of messages synced to the computer.
How do I change the Mail to keep offline setting for everyone in the organization?
This setting is in the Outlook 2013 Group Policy templates and stored in the registry. In the Group Policy editor, it's under Microsoft Outlook 2013, Exchange, Cached Exchange mode. Look for Cached Exchange Mode Sync Settings.
If you prefer to set the registry key using a logon script, you need to set this key:
Value: Valid values are 0, 1, 3, 6, 12, or 24
Use a decimal value equal to the number of months. Use 0 for All messages.
Decimal Value: Valid entries are 0, 1, 3, 6, 12, or 24 (in months).
Decimal Value: Valid entries are 0, 3, 7, or 14 (in days)
Set both values to 0 to sync all; otherwise the one not used should be set to 0.
Only a subset of your Exchange mailbox items are synchronized in Outlook 2013 (MSKB)