Are you using the free version or trial of that SysTools software? If so, maybe it has limitations to get you to pay for a full version. I'm not familiar with it, and it seems they are keen to play down the ImportExportTools NG add-on, which on the other hand, I am familiar with and have used without any of the mentioned issues. Development of the add-on stalled for some time, but it got revived and is currently compatible with the latest release version of Tbird (68.8.1). I suggest you give that one a try. Create a local folder into which the mbox will be imported, then use the ImportExportTools NG add-on to import the mbox into that folder and see how it goes.

Hello Dan,

Thanks for your answer, I am using the full version of the SysTools software and there is data present into the MBOX files as I am checking with the SysTools MBOX Viewer software.

Also, I have copied MBOX file into the Thunderbirds local profile, in the MBOX file there is mails and I am getting a problem for some of the mails not for all mails. Here I am trying to upload my sample MBOX file but there is no option. If you share your email-id then I will share a sample file with you.

Best Regards, Rupesh

You can upload that sample file to a file sharing/hosting service of your choice, for example: Google Drive, then copy the link here in your next reply.

Please find sample file using the below link - https://downloads.systoolsgroup.com/installer/MBOXSampleSupport.zip

Please do let me know if you need anything from my end.

In this sample file there are total 3 mails but in Thunderbird I can see only 2 mails.

Yes, there are three messages in the mbox file, but only two are imported. The one that isn't imported has the X-Mozilla-status header bits added to it. These header bits are used by Thunderbird to mark messages as read, deleted, etc. The two header bits applied to that message are:

X-Mozilla-Status: 0008

X-Mozilla-Status2: 00000000

If you delete those two lines from the mbox file (using a text editor like notepad), then the marked message will get imported as expected.

See http://forums.mozillazine.org/viewtopic.php?f=39&t=3029994

Thanks Dan for your quick help!! Much appreciated!! After deleting those two lines from the MBOX file I am able to see the mails inside the Thunderbird.

You're welcome. It is Stans FYI, not Dan.

Ohh sorry my mistake, Thanks, Stans :)

No worries.