If you added a large email account to the Outlook email client, you may experience application pauses. The larger the data file, the more application pauses you may experience. The data files may be either personal folders (.pst) files or offline folder (.ost) files. To resolve this problem, reduce the size of your data file by moving or archiving items from the file.
If you have a large email account, you may experience application pauses while you perform typical operations in the Outlook email client. These typical operations include reading email messages, moving email messages, and deleting email messages.
The following list summarizes expected behavior based on the size of your email account:
- Up to 5 GB: This file size should provide a good user experience on most hardware.
- Between 5 GB and 10 GB: This file size is typically hardware-dependent. Therefore, if you have a fast hard disk and lots of RAM, your experience will be better. However, slower hard disk drives, such as drives that are typically found on portable computers or early-generation solid-state drives (SSDs), experience some application pauses when the drives respond.
- More than 10 GB: When the .ost file reaches this size, short pauses begin to occur on most hardware.
- Very large (25 GB or larger): An .ost file of this size increases the frequency of short pauses, especially while you are downloading new email messages. However, you can use Send/Receive groups to manually sync your mail.
You may consider using synchronization filters for Cached Mode profiles to reduce your .ost file size in the Outlook email client. You can find more information on how to reduce the size of your local data file by using synchronization filters here. This is a stopgap solution and is provided here for reference if you cannot reduce the size of your mailbox. For example, you may be unable to reduce the size of your mailbox if you have to maintain an archive of all sent and received email messages over a span of several years.
For Outlook 2013 and later versions, you can also try to use the Sync Slider feature for Cached Mode profiles in the Outlook email client. This feature lets you control how many months of email messages are synchronized with your .ost file. You can find more information about the Sync Slider feature here.