Outlook Data File Performance
If you have a large .pst or .ost file, you may experience application pauses while you perform typical operations in Outlook. 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 Outlook data file.
- Up to 5 GB: This file size should provide a good user experience on most hardware.
- Between 5 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. For more information about Send/Receive groups, see the “Are you synchronizing many RSS feeds?” section.