Rated 4 out of 5 stars

le tommyzulu ar MFómh. 13, 2011 · buan-nasc

This works for me really well. (Thunderbird 6.0.2). I cut and pasted a list of many emails from an Excel workbook into the top address box and hit the 'enter' key as per the instructions and hey presto! it worked a treat. I did it again using, selecting "Bcc" and the emails were sent to 'undisclosed receipients'.
I would recommend it to anyone who has lists of emails.