As of February 2010, AOL email accounts no longer automatically store sent messages in Thunderbird's Sent message folder. However, you can manually configure Thunderbird to do this:
- In Tools > Account Settings..., select your AOL account from the list on the left and then select the Copies & Folders page.
- In the top section of the page, check the "Place a copy in" checkbox, and then click the Sent Folder on option.
- In the drop-down list to the right, select your AOL e-mail address.
- Click OK to save the changes.