Delete Unsent Messages in Thunderbird

Thunderbird is great, but it does have a have few quirks.

If you "Send Later" your message will be placed in your Outbox and you will be prompted to send unsent messages next time you start up Thunderbird. But let's say you decide you don't want to send that message after all. Well, supposedly, you go to your Local Folders -> Outbox folder and delete the message. Unfortunately this did not work for me (Thunerbird 3.1.11) - I could see no messages in the Outbox, yet it still prompted me to send unsent messages each time I started Thunderbird. The simplest solution I could find is right-click Outbox -> Search... Search on something to do with the email, e.g. From your email address and it will list all messages in the Outbox, select the one you wish to delete and press the Delete button.

BTW, standard "Send Later" is not particularly advanced functionality, so instead I suggest you use the Send Later 3 add-on.