Cannot use ost saved file reinstalling account in outlook 2016 for windows

Copper Contributor

I have Ms Outlook 2016 on win 10

I had MS Outlook hanged, It did not downloaded incoming mails. 

After some various and unsuccesful attempts to solve the problem I saved Ost and Pst files (both about 4 gb) in a usb dongle, then I  deleted my account from outlook, and deleted the ost file from the relevant directory.

Then I  re-inserted my gmail account in outlook and over written the ost file in the relevant  directory with the previous one saved on dongle, that have the very same file name. 

I did expected to see my in and out mail archive at the first outlook opening; instead outlook give a massage that the archive is not a valid one.

What is wrong with my procedure and how can I have the sent mail archive back from the ost file (incoming masseges are not a problem since is a IMAP)?

Thanks a lot for any solution, at the moment I have lost 4000 sent massege.


6 Replies

Hi frktest,

The OST-file is an Offline Outlook Data File that downloads all of part of the emails from the mailserver (offline caching). You can not reuse this file. Only a PST-file can be used.

I would recommend starting from a freshly created OST file and let the Outlook Desktop App download the emails from the mailserver.


Also check in the Outlook Desktop App: View > Change View > IMAP Messages if emails are seem to be missing.


Regarding backups, please note that it is important to check that the Microsoft Desktop App did download ALL emails from the emailserver before exporting them to a PST-file.



Thank you very much for your response.

Since my email address is and outlook was set to IMAP I have no problem with incoming messages as they are saved on gmail server.

The problem I'm trying to solve is that I  lost all sent messages (about 4000).

If I cannot reuse OST file there is a way to recover them? 

Actually I was confident to be on safe having saved a 4 GB data OST file.

When you say to let the Outlook Desktop App download the emails from the mailserver, do you mean that it will download sent messeges again too?


Thanks a lot for your help


Hi frktest,


IMAP wil also sync the sent items from the mailserver.

When you open a browser and sign-in to, are all missing sent items available there?

No, because the sent messeges have been written and sent with outlook.
You can try to repair the OST with third part software.
You were right about gmail mailserver, actually the sent messeges are there also and I was able to synchronize in outlook. Thanks for your help.