Backup email
After locating your email profile (how to find your Thunderbird profile), close Thunderbird
Then copy your profile folder to another location. This could be your desktop or an external drive.
Make sure to make a note of the location so you can easily find it if something goes wrong.
Remove the .msf file for the problem folder
Go into your profile folder, and then into the Mail folder inside it. In the Mail folder there will be Local Folders and probably a folder called “mail.iam-afghanistan.org”
If the email folder that has the problem is in Local Folders, go into the Local Folders.
If the email folder in an account folder, go into the mail.iam-afghansitan.org folder.
Inside the folder, there are two files for each folder you have in your account. For example:
Inbox and Inbox.msf
For the email folder with the problem, delete the .msf file. Do not delete the other file.
Reopen Thunderbird
Start Thunderbird. It may take some time, if you had a lot of email in that folder.
Check to see if the email is restored.
If mail is properly restored you can delete the copy of your profile folder you made at the start of this process.