How to reduce the size of Outlook data files (.PST and .OST)

After a long time of use, your Outlook mailbox will "fill up" significantly. So every time you open Outlook, the open process will take place very slowly, or there are many errors, even Outlook will hang.

Is there any way to reduce the size of data files in Outlook? Please refer to the following article of Network Administrator.

1. Manage your mailbox

Mailbox Cleanup is one of the useful tools used to view your mailbox and personal folders on Outlook.

Alternatively, you can store old messages in Outlook Data File (.pst) to empty the Deleted Items folder.

1. Click the File tab .

2. Click on Cleanup Tools .

3. Click Mailbox Cleanup .

4. Follow the steps below:

- To see the total mailbox size and any folder, click View Mailbox Siz e.

- To find old messages, select Find items older than n days , enter any number between 1 and 999, then click Find.

- To find large messages, select Find items larger than n kilobytes , enter any number between 1 and 9999, then click Find .

- To delete old messages in your mailbox to store in Outlook Data File (.pst), click AutoArchive.

Outlook Data Files (.pst) are stored in the D ocumentsOutlook Files folder on your computer. If you use Windows XP, the .pst file is saved in the My DocumentsOutlook Files folder.

- To view the size of the Deleted Items folder , click to select View Deleted Items Size .

- To "empty" the Deleted Items folder , click Empty .

- To see the size of the Conflicts folder, click View Conflicts Size .

- To delete the contents in the Conflicts folder, click Delete .

2. Reduce the size of Outlook Data File (.pst)

If you delete items in Outlook Data File (.pst), the files will automatically be compressed on the background when Outlook is running but you are not using the computer.

Also you can compress these items manually. The Outlook Data File (.pst) compression process will take a few minutes.

1. Delete any items that you do not want to store.

2. Open the Folder List view.

In the bottom corner of the Navigation Pane, click the Folder List icon or press Ctrl + 6 .

3 On the Navigation Pane interface, right-click the Deleted Items folder , and then click Empty Folder .

4. Click the File tab .

5. Click Account Settings , and then click Account Settings .

6. On the Data Files tab, click to select the data file you want, then click Settings .

7. Click Compact Now .

Note:

You do not need to exit Outlook after compressing the Outlook Data File (.pst).

3. Reduced Outlook Data File Offline (.ost)

Reducing the size of an .OST file greatly improves Outlook performance. This process does not delete any mail, and any saved items are running Microsoft Exchange Server on your computer.

1. Delete any mail, items that you do not want to store.

2. Open the Folder List view.

In the bottom corner of the Navigation Pane, click the Folder List icon or press Ctrl + 6.

3 On the Navigation Pane interface, right-click the Deleted Items folder , and then click Empty Folder.

4. Click the File tab.

5. Click Account Settings , and then click Account Settings .

6. On the Data Files tab, click to select the data file you want to compress, then click Settings .

7. Click Compact Now.

Note:

- To delete items from the online and offline folders, select the items then select Delete.

- If you are using Cached Exchange Mode Exchange account, you can only select to delete items in the offline Outlook Data File folder (.ost).

- By default, when you use Cached Exchange Mode, your favorite public folders will not be synchronized.

If you choose to synchronize public folders, the .OST capacity will increase significantly.

Refer to some of the following articles:

1. Instructions for adding Gmail accounts to Outlook 2013 and 2016 using IMAP

1. Microsoft Outlook acceleration tips

1. All problems with PST, Profile, Add-in . errors on Outlook and how to fix them

Good luck!