While browsing, I found this post, hope that you will find it useful too..
https://sysc.org/remove-ost-file-password/
The post suggests manual procedure to recover data from a password-protected OST file by dismounting and moving it onto a new machine. While performing the method you may be asked to check for any integrity issues with your OST file to be on the safer side. So before dismounting OST on a new machine, take a backup & then proceed further.
When digging through the post I found an application for removing password from OST files. I personally tested the suggested OST Password Recovery tool on my machine & found it to be quite impressive in terms of both; efficiency and integrity. Therefore, I would recommend this solution as 100 percent safe & guaranteed.