What to do if the size of your Outlook data file increases over time and causes issues

To resolve this issue, create several new Personal Data Files (PST) files to manage your email messages.

If you are using Outlook 2010 or 2013 follow these steps to create new PST files: 

1. Click Start, type Mail in the search box, and then click Mail to open the Mail Setup - Outlook dialog box.
2. Click Data Files.
3. In the Data Files tab, click Add.
4. Type a name for the PST file. For example, Family, and then press Enter.
5. Then you notice a PST file is created in the Account Settings dialog box.
6. Click Add again to create more PST files. For example, Friends, Colleagues, and so on.
7. Once you finished, close the Mail Setup dialog box.
8. Click Start, type Outlook in the search box, and then click Microsoft Outlook 2010or 2013 to start Outlook.
9. You will notice all PST folders present in Outlook. Now, you can move email messages from the main data file to these PST folders.

Video: How to create new Personal Data Files (PST) to manage your email messages