I have always had .PST for my home email file, now I changed IPSs and set up my account and it's an .OST file--I had no say in the matter nor did I have a say in the name of the file, which I'd like to change but can't. I don't know much about the difference, all I know is the old ISP was a POP3 and the new one is IMAP.

I guess my question is--is that the difference--for POP3 Outlook uses .pst and for IMAP it uses .ost? And are they mutually exclusive?

Thanks, Jim

  • Yes. PST downloads and keeps the e-mail on your computer. For OST, the mail remains on the server, but only have a cache. If your computer crashes, the you can use another computer and download the e-mail again. For PST, if your computer dies, those e-mails are lost with the computer. Better to have for flexibility and safety. – Sun Jun 6 '16 at 20:51

.OST is generally used for offline access to Exchange email accounts. It syncs up with the Exchange Server when you have an internet connection so that you can still access your email when you are offline.

.PST is a filetype that is used for POP3 and IMAP to download email from the server for archiving. If you opt not to leave a copy on the server then you do not have access to the emails from web apps such as Outlook Web Access.

The email address at your new ISP is most likely a hosted exchange account, thus the reason for the .ost.

For more in depth information on the difference between a .ost and a .pst file you can visit Microsoft's Support Site.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.