Cannot open Outlook Data File

[jmt356]

I am trying to open a backup of an Outlook Data File (.ost). When I double click on the Outlook Data File, Windows prompts me to choose a program to open it with. When I choose Outlook.exe, I get this error:

"The program you have selected cannot be associated with this file type. Please choose another program."

When I try to open the file from within Outlook, I get an error that states:

"The file you chose is not an Outlook Data File. You must select a new file of this type."

I am having this issue with two Outlook Data Files. One is an .ost file and the other is an .nst file. I know they are both Outlook Data Files because I can see this in their properties. However, Outlook does not recognize them as Outlook Data Files. When I go to Open Outlook Data File, they don't show up when I have Outlook Data File as the file type. They only show up when I choose All Files as the file type.

How do I open it?

[Leif]

https://support.microsoft.com/en-gb/off ... 458afc5253

[HansV]

And according to Introduction to Outlook Data Files (.pst and .ost):

Outlook Group Storage File (.nst)

The first time you access a Group in Outlook, a new type of Outlook data file is created. This file has an extension of .nst, and stores your Groups conversations and other local Groups data. All of this information is synchronized between your computer and the email server, so there is no need to back up this file or import it when you set up Outlook on a new computer.

[jmt356]

Does anyone know how to open an OST in Outlook? I don't need to repair the .ost file. I just need to know how to open it.

File | Open Outlook Data File can only be used to open .pst files. I am trying to open an .ost file. No .ost files show up in File | Open Outlook Data File. This is true even for perfectly healthy .ost files.

[HansV]

Open or import items from an offline Outlook Data File (.ost)

Steps to open and view Outlook OST files

[jmt356]

I reviewed the first link ("Open or import items from an offline Outlook Data File") before I started this thread. That page is useless. It doesn't explain how to open or import items from an offline Outlook Data File. Rather, it explains how to recreate an offline Outlook Data File (.ost). I am not interested in recreating my Outlook Data File. I just want to open it in Outlook.

The second link states as follows:

"It is important to note that the OST file is specifically tied to the Exchange Server mailbox profile. As a result, you cannot simply load an OST file into Outlook or open it with a different Exchange Server mailbox profile. If you create a new Exchange profile, Outlook generates a new OST file, leading to the complete loss of unsynchronized changes from the previous file.
"In this article, we will delve into how to open an OST file in Outlook and how EdbMails can help you open, preview, and convert an OST file to a PST when it becomes orphaned or corrupted."

As I read this, if a user does not have an active email account in Outlook associated with an .OST file, the user cannot open that .OST file. The user must use third-party software to convert the .OST file to a .PST, which Outlook can then open and read.

I find this senseless. How can MS develop an application that creates a certain kind of file that then cannot read those files without the use of third-party software?

I recall years ago whenever I had an issue reading an .OST file I could change the name or move the location or even move it to another computer and then open it in Outlook to view it, whereas now, if an .OST is not actively synchronizing with an email account or is not converted to a .PST, it cannot be viewed.

I assume this is because MS doesn't want an unauthorized user to gain access to another person's .OST file and then view its contents, so MS locks it down. Users don't need to be babysat in this way. They can be trusted to protect their data with passwords and to encrypt their hard drives and use passwords in Windows. And if that is MS's logic, why not also prohibit users from viewing .PST files on computers that are different from the ones they were created on?

[StuartR]

An OST file is a local store of data on an Exchange server. Responsibility for the security of the data is typically owned by the corporation that owns the Exchange server, not the individual user.

[HansV]

A .pst file is THE mail storage. There is not necessarily a copy of the items that it contains on a server. It is not tied to a particular account. You can give a .pst file to someone else.
A .ost file is basically a local copy of items of a specific account stored on a server. If you log in to the account associated with the same account on another computer, Outlook will automatically create the .ost file there.

[jmt356]

But I have an .OST file that is floating on my hard drive from an account that I closed. That account is no longer active and I deleted the account from the list of accounts in Outlook (I deleted the account because each time I launched Outlook, I was prompted for a password but I could not enter a password that was accepted because the account was deactivated, but i could not access my other Outlook accounts without resolving the prompt for the password on the deactivated account). Deleting the account did not delete my .OST file. I find it counterintuitive that Outlook cannot now open that .OST file. Do I need to install third-party software to convert the .OST file to a .PST file before I can view the .OST file? I believe years ago I could copy an .OST file to any company and view its contents without converting the .OST file to a .PST file.

[HansV]

As far as I know, you do need a third-party utility too open/convert an "orphaned" .ost file.

I've never had this problem myself, so I don't know if it ever was possible natively.

[StuartR]

When I had to use an Exchange server, I regularly created a PST file, copied the entire content of my OST file to the PST file and then dropped the PST file from my profile. This gave me a structured copy of all my data in a form that I could easily open without needing access to the server.

[jmt356]

When I had to use an Exchange server, I regularly created a PST file, copied the entire content of my OST file to the PST file and then dropped the PST file from my profile. This gave me a structured copy of all my data in a form that I could easily open without needing access to the server.

It's absurd that MS requires such a convoluted process to open an OST file. Outlook was created to view OST files. It should be possible to open one in the same way one opens PSTs. It's unreasonable to require users to convert an OST to a PST or download third-party software to view an OST.

[SpeakEasy]

An OST is in the end simply just a local cache, it's not meant for data retrieval, it is not designed to be directly opened and accessed by the end user. It never has been. And Microsoft documentation has been clear on this for many years, since at least 1997.

That being said, it continues to surprise me that MS have never made an OST recovery or conversion tool available, and advise the use of any of the many 3rd party tools OST2PST tools

[jmt356]

I think that when you characterize it that way, it is more reasonable. Btu I still think MS should make it more user friendly.