Sorry, confused this thread with a different question!

As far as I can tell, Thunderbird does not have a built-in "AutoPreview" feature which can show the beginning of the message body in the inbox.

There may be a tooltip when you hover over the line in the Inbox, but that is a lot slower than having the text there automatically.

The text may appear in a notification pane pop up that shows your newest messages, but that is transitory and doesn't help for older messages.

So, I guess you would need an extension to add this, if such an extension exists.

Hi sfhowes, thanks for noting that. I've only noticed it when filtering and filing stuff into folders and didn't think to try using it for other purposes.