.ost
file) on the user's computer, together with an Offline Address Book (OAB).Issue | Description | Resolution |
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Synchronization delays and issues with shared mailboxes, including shared calendars and mail folders. | By default, if an Outlook profile is configured with an Exchange account using Cached Exchange Mode and you add an additional Exchange mailbox to the profile, all items in all the folders to which you have access in the additional mailbox are downloaded to your offline Outlook data ( .ost ) file).These shared secondary mailboxes being cached can cause synchronization delays when delegates make updates to shared calendar items (including creating/editing meeting requests and appointments) and mail folders. | You can disable caching of additional mailboxes by following these steps:
Shared mail folder caching can also be disabled using the Office Customization Tool (OCT) or Group Policy; see By default, shared mail folders are downloaded in Cached mode in Outlook 2010 and later versions. |
Outlook for Mac versions experience synchronization delays with shared folders and calendar items. | Outlook for Mac desktop versions (including 2016) support only Cached Exchange Mode. Because the clients operate in this mode, this sometimes causes synchronization delays between the client and the Exchange server. | For Outlook 2016 for Mac, you can try to resolve the issue by resetting the cache for the unsynchronized folder or calendar; see Clear the cache in Outlook for Mac. |
Only a subset of your Exchange mailbox items are synchronized in Outlook 2016 or Outlook 2013. | The email folders for these mailboxes may show item counts that are lower than expected. Additionally, older items seem to be missing, and you receive the following message at the bottom of the list of items: 'There are more items in this folder on the server. Click here to view more on Microsoft Exchange.' | This behavior occurs because the Cached Exchange mode Mail to keep offline setting is configured to a value other than All. In the default configuration, depending on the size of your hard disk, Outlook synchronizes only 1, 3, or 12 months of email to your offline data ( .ost ) file from the Exchange server.This setting does not affect the number of items that are synchronized with folders of the following types:
For more, see Only a subset of your Exchange mailbox items are synchronized in Outlook. |
Performance issues when there are too many items or folders in a Cached mode offline data ( .ost ) file or Outlook data (.pst ) file folder. | When you use Cached Exchange Mode or an Outlook data ( .pst ) file and you have a lot of items in any single folder, you may experience symptoms like the following in Outlook:
| This problem may occur if you have folders that exceed the limit for the number of items per folder or if you have too many folders total. The item and folder limits depend on the version of Outlook, as follows. Outlook 2016, Outlook 2013, and Outlook 2010:
If you have folders that exceed the limit for the number of items in an Outlook data ( .pst ) file or an offline Outlook data (.ost ) file, move items from the larger folders to separate or smaller folders in the same mailbox or data file; see Outlook performance issues when there are too many items or folders in a Cached mode .ost or .pst file folder. |
When you are using Cached Exchange Mode, a message may remain in the Outbox for up to one minute until the next synchronization with the Exchange server occurs. | To send a message immediately, click the Send/Receive tab, and then click Send All. For more, see Plan and configure Cached Exchange Mode in Outlook 2016 for Windows. |