This doesn't directly solve your issue but...
You can make Thunderbird use an Outbox folder so that it doesn't immediately send the messages. Then you could review the Outbox before sending.
In the Write window, when you have complelted the message, instead of clicking send, either go to File, Send Later or simply hit "CTL+SHIFT+RETURN".
Alternatively install the MagicSLR extension and put a Send Later button in the Write window's toolbar.