PST is the only file extension of Outlook. It is one of the oldest file formats and is widely accepted to use for both professional and personal purpose. If you want use Outlook, MBOX file extension is not supported by the email client, conversion is must. Outlook supports OST and PST. The Personal Storage Table is a common outlook format. It could be beneficial for you using the extension. It has capacity to store data up to 50 GB. It allows you to store files in the hard drive.