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The May 3, 2016, update for Outlook 2016 allows administrators to set additional values for the Mail to keep offline. This setting is sometimes referred to as the Sync Slider. 

In addition to the existing windows, administrators can now add 3 days, 1 week, 2 weeks, 36 months, and 60 months to the default Mail Sync Slider windows for new Exchange accounts in Outlook 2016 by setting the SyncWindowSettingDays registry value. If the override registry value setting is configured, Outlook 2016 will correctly prefer it instead of the disk size when it determines the default Sync Slider windows for new Exchange accounts.

Note Before this change, the default Sync Slider windows for new accounts could be configured only manually by setting the SyncWindowSetting registry value. This change introduces a new registry value that lets administrators select 3 days, 1 week, 2 weeks, 36 months, or 60 months as the default settings in addition to the existing options of 1 month, 3 months, 6 months, 12 months, 24 months, and All.

More Information

To change the default Sync Slider windows for new Exchange accounts, install the May 3, 2016, update for Outlook 2016 (KB3115101) and April 3, 2018, update for Outlook 2016 (KB4018326), and then follow these steps.

Important
Follow the steps in this section carefully. Serious problems might occur if you change the registry incorrectly. Before you change it, back up the registry for restoration in case problems occur.

1. Exit all Microsoft Office applications.
2. Start Registry Editor:
   • In Windows 10, go to Start, enter regedit in the Search Windows box, and then select regedit.exe in the search results.
   • In Windows 8 or Windows 8.1, if you’re using a mouse, move it to the upper-right corner, go to Search, enter regedit in the search text box, and then select regedit.exe in the search results.
   • In Windows 7, go to Start, enter regedit in the Search programs and files text box, and then select regedit.exe in the search results.
3. Locate and then select the following registry entry:
   HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Cached Mode
4. On the Edit menu, point to New, and then select DWORD Value.
5. Enter SyncWindowSettingDays, and then press the Enter key.
6. If the SyncWindowSetting value does not already exist, point to New on the Edit menu, and then select DWORD Value.
7. Enter SyncWindowSetting, and then press the Enter key.
8. In the Details pane, press and hold (or right-click) SyncWindowSettingDays or SyncWindowSetting, and then select Modify.
   
   Note Both the SyncWindowSetting and SyncWindowSettingDays registry values should be set correctly to make sure that Outlook 2016 selects the correct window. If one of the registry values isn’t configured, or if it is set to an invalid value, Outlook 2016 sets the default value of 12 for the SyncWindowSetting registry value and 0 for the SyncWindowSettingDays registry value.
9. To set the value for the SyncWindowSetting and SyncWindowSettingDays registry keys, see the following table for more information.
   

Desired sync window	SyncWindowSetting value	SyncWindowSettingDays value
3 days	0	3
1 week	0	7
2 weeks	0	14
1 month	1	0
3 months	3	0
6 months	6	0
12 months	12	0
24 months	24	0
36 months	36	0
60 months	60	0
All	0	0

10. Note If you use the Outlook 2016 administrative template to configure the Cached Exchange Mode Sync Setting policy to 1 week, 2 weeks, or All, the Group Policy Management Console (GPMC) always shows 3 days when you open the management console again. However, this affects only the way that the setting is displayed in GPMC. Actually, the Cached Exchange Mode Sync Setting policy works correctly as configured.
11. Exit Registry Editor.