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Applies to:
Outlook for Microsoft 365, Outlook LTSC 2021, Outlook 2019, Outlook 2016, Outlook 2013

If you have to change the number of selected months of email to synchronize with your cached mode “.ost” file, follow these steps:

1. Start Outlook.
2. On the File tab, click Account Settings, and then click Account Settings.
3. On the E-mail tab, double-click your Microsoft Exchange account.
4. In the Change Account dialog box, drag the Mail to keep offline slider to the desired number of months or to All to synchronize all email messages.
   
5. Click Next.
6. Click OK when you’re prompted to restart Outlook to complete the configuration change.
7. Click Finish.
8. Restart Outlook.

Working Offline

If you don’t have connectivity with the Exchange server, the following message is displayed in a folder if there are older items on the server that were not synchronized with your .ost file:

There are more items in this folder on the server

Connect to the server to view them

This message is shown in the following screenshot.

Under similar conditions, if you search for items in your mailbox and you don’t have connectivity with the Exchange server, the following message is displayed below the search results:

Server unavailable. <x> months of results shown.

In this message, <x> represents the value that’s configured for the cached mode Mail to keep offline setting.

An example of this message is shown in the following screenshot.

This problem will only be resolved when you have online connectivity, so make sure when you restart your outlook you have connectivity.