Try to rebuild the index file of the troubled folder. Right-click the folder - Properties - Repair Folder

Thanks, but this didn't work.

What is your account type - POP or IMAP?

What is the size of your Inbox?

Do you have a backup of your Thunderbird profile? If not, create one.

http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Backing_Up_and_Restoring

It is a POP account.

I just backed up the profile.

I don't know the size of the inbox nor how to see what it is nor change it. However, the inbox for this account is currently empty. (Yes, I know this post is about not being able to delete emails from the inbox, so how can it be empty? In my research I found a post of someone with the same problem who discovered he could move emails from the inbox to another folder and then delete that folder (not the individual mails in the folder, but only the entire folder). That is how I emptied the inbox, but it is a very cumbersome work around that I shouldn't have to do.

Ok, then compact Inbox:

Right-click Inbox - Compact

It's recommended you enable automatic compacting. More information about compacting in this article.

http://kb.mozillazine.org/Compacting_folders

I'd not expect anymore problems with deleting messages after compacting.

If you still have problems, follow these instructions.

http://kb.mozillazine.org/Compacting_folders#Real_fix

I don't know why this worked but it did. To summarize the solution: 1. I created a new folder in the email account. 2. I moved all emails from the inbox to this folder. 3. I deleted this folder. I then had an empty inbox. 4. I compacted the now empty inbox.

I am now able to directly delete emails from the inbox. Thank you Christ1 for your help.