Saving and using pst-files on an external USB-drive

Yes, using a pst-file from a USB-drive is supported but still not recommended.

With some additional knowledge and precautions, it is possible to use it in a safe way and not risk any data loss.

Performance concern

While there are no reading/writing issues similar to connecting to pst-files on a network share (which isn’t supported!), external drives are often slower and/or have power saving features which could interrupt or slowdown Outlook performance.

With USB 3.0 hard disks, the performance issue is basically gone. For USB-sticks (or flash-drives), this isn’t always the case as they usually struggle more with multiple read/write operations at the same time.

Close Outlook before detaching

Another (and even bigger!) concern is that Outlook requires continuous access to a pst-file. When Outlook loses the connection to a pst-files while Outlook is still running, the pst-file could get damaged.

In order to prevent this, you must always remember to first close Outlook before shutting down or detaching your external drive. If you forget to do this, you can use scanpst.exe to check your pst-file for errors.

Detach pst-file after every use

When you connect to a pst-file, Outlook will add a reference to this pst-file to your mail profile. The next time you start Outlook it will automatically try to open the pst-file again. If you would open Outlook when the file is missing, because the external drive is detached, you could end up with several error notifications about the missing pst-file or even end up corrupting your mail profile.

To prevent this from happening, it is recommended that you detach the pst-file from the Outlook mail profile after each use. You can do this via;

• Outlook 2007
  File-> Data File Management…-> select pst-file-> Remove
• Outlook 2010 / 2013 / 2016 / 2019 / Microsoft 365
  File-> Account Settings-> Account Settings…-> tab Data Files-> select pst-file-> Remove

Note: The lock on the pst-file will still be kept. Before detaching the external drive and to fully release the lock on the pst-file you must still first close Outlook.

Don’t forget; make a backup!

Especially when you travel with your external drive, external drives are often a bit more prone to get damaged, lost or even stolen. Even when you have it placed on your desk, remember that it is a (smaller) separate unit which could get damaged by falling a lot more easier than an internal drive.

Combined with the above remarks about the pst-file getting damaged a lot easier than when placed on an internal drive, making frequent backups of your pst-files is even more important when using a pst-file from an external drive.