https://support.microsoft.com/en-us/help/2752583/you-cannot-change-the-location-of-the-offline-outlook-data-file-ost-in

• Copy the existing .ost file to the new location that you want to use. If you want to create a new .ost file isntead, you can skip this step.
• Open Control Panel. Open the Mail applet.
• Click Show Profiles → Add
• Add the Exchange account using email address and password.
• Stay in the Add Account window after successfully adding.
• Tick the Change account settings box → Next
• Click More Settings…* → Outlook Data file Settings… * Click Browse then browse to the OST file you copied in step one or the location you want the OST in. * Type the name for the new OST file and click Open → Finish

https://www.nucleustechnologies.com/how-to/change-ost-location.html |

These images are from the free Thunderbird mail client, but they illustrate the basic configuration. Thunderbird is great for POP or IMAP accounts.