From last few days, my PC is not working properly. So, I have decided to upgrade my System. After upgrading my system, I transfer all data from old system to new system but in present time I am unable to access my mails. I have checked every possible detail but I didn't find anything wrong about it. While checking database of my mails I found .ost file which is inaccessible right now. So, please let me know how can I get back my emails? Thanks in advance.
oh so your main problem is that your .ost file becomes inaccessible, so let me tell you that .ost file is a highly secure file and while your outlook creates .ost file as a mail backup at that time if you change your system or change current profile, your .ost file becomes inaccessible because of security reason so in this case you need to convert your .ost file to .pst file format. for further information please read this article https://sites.google.com/view/whyneedosttopstconversionandho/home
If your same profile is not configured with Exchange Server, then you can not open the OST file directly. So I want to recommend, there is no successful manual method available to convert OST file to PST format. You should choose any third party solution, which easily convert your data with all data properties such as contact, calendar, to-do list, etc.
Here some websites, where you can pick this converter
Aryson, MailsDaddy, MailsSoftware, Datahelp etc.