Yes, it was deleted permanently.

TB is now telling me that the "permanent" deletion is still on the disc. If so, how do I recover it?

Do not compact any folders.

In Thunderbird

• 'Help' > 'Troubleshooting Information'
• click on 'open folder'

a new window opens showing profile folder name

• Close Thunderbird now - this is important
• If this was a pop account - click on 'Mail' folder
• click on pop mail account name that has missing emails.

you should see the 'Inbox' mbox file - it has no extension. I'm not sure what folder the delted message was originally in, but there will be an mbox file for that folder name. So assuming it was the 'Inbox'.

• Open the 'Inbox' file using Notepad

Emails are written to the file one after the other, so oldest will be at the top and newest at the bottom. Each email will start with these lines: this is an example

• From - Sun Dec 28 18:14:40 2014
• X-Mozilla-Status: 0001
• X-Mozilla-Status2: 00800000

Use 'Edit' > 'Find' Try to locate the deleted email, by searching for the Subject or part of the email address etc.

When you have located the email: Look for this line: X-Mozilla-Status: (not X-Mozilla-Status2:)

   Make sure the X-Mozilla-Status: has the number 0001
   Save the file.
   delete the 'Inbox.msf' file. A new one will be auto created.
   Restart Thunderbird. 

If this recovers any emails in Inbox where you altered that X-Mozilla-Status to 0001.

What if the X-Mozilla-Status has the number 0009? Should I change it to 0001? How do I select the file in order to save it since it is only one of hundreds in the Inbox folder? Where should it be saved?

What if the X-Mozilla-Status has the number 0009? Should I change it to 0001?

Yes. 0009 means it has a 'deleted' marker.

re: How do I select the file in order to save it since it is only one of hundreds in the Inbox folder? You have already opened the mbox file to see the contents, so after making the 0001 alteration, you just save the file - not save as. Use: 'File' > 'Save'.