Change how much mail to keep offline

With a Microsoft Exchange Server account, you can decide how much mail is available when working offline with a slow or no network connection.

  1. Click File > Account Settings > Account Settings.

    Account Settings in the Backstage view

  2. Select an Exchange account, and then click Change.

    Change command in the Account Settings dialog box

  3. Under Offline Settings, move the slider to the desired amount of time, such as All, 12 months, 6 months, 3 months, or 1 month.

    Offline mail storage amount slider

    For example, if you move the slider to 3 months, only mail from the past three months will be synchronized to your Offline Outlook Data (.ost) file from the Exchange server. Items older than 3 months reside only in your mailbox on the server. You can change this setting at any time.

    Cached Exchange Mode, which downloads a copy of your messages, must be turned on.

By default, Outlook configures Exchange accounts to only synchronize a specific number of months, depending on the size of the disk. The following table shows the default Sync Slider setting for different disk sizes:

Disk size

Default setting

Smaller than or equal to 32 GB

1 month

Greater than 32 GB, but smaller than 64 GB

3 months

Equal to or greater than 64 GB

1 year

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