Relink an existing OST file with IMAP/POP account setup

To relink an existing orphaned OST file with the IMAP/POP server account that do not have a PST file, only the OST file is available.

According to your description, As I understand that your emails were stored in an original .ost file and you would like to re-access them in a new environment with imap or pop account, is it right?

If so, please first understand that OST files could only be opened/accessed via the email account used to create it in a given profile, and recreating the same email account does not “re-use” an existing OST file, which means we couldn’t access the original .ost file directly with a new profile in outlook.

For your requirement, I have tried to researched some workarounds about it and found many users recommend us to convert the .ost file to .pst file via some tools, so that we could open/access .pst file in Outlook.
It’s suggested to search for some convert tools for your need, and for your reference, here are some tools that I found about converting an .ost to .pst: Convert an Offline File (.ost) to a Personal File (.pst)

Just a clarification, OST files are offline files that you can access your emails without having a direct connection to the exchange server from the last synchronization, that is, outlook accesses your emails since the last synchronization offline (called mode cache). If the emails are deleted from the server, the moment the outlook reconnects to the server, those emails will also be removed from the OST file, so it would not work in a very effective way for security as you are placing.

The way you are trying to work would be via PST files, where it downloads messages to the file from the server, and even if you delete these messages from the server, they will remain in the file in question, so it would serve what you are looking for .

So Finally:

There is no way to relink the orphaned OST file again with the IMAP/Exchange server. OST file is a highly encrypted file bound with the secrete key with the Outlook account. To access the OST file with the Outlook account, it must match both secrete keys. In case of a mismatch, the OST file does not respond to the Outlook account.

However, there is no free or manual trick to access that OST file in Outlook again. But with help of 3rd party OST Conversion tools, You can convert the orphaned OST file in the PST format that could easily import into the Outlook account effortlessly.

I did little research to find OST to PST tools and found the following threads:

https://www.stellarinfo.com/convert-ost-to-pst.php

https://www.kdetools.com/ost-to-pst-converter.html