Thunderbird question

[wayward4now]

When I send a message, instead of the process happening in the 
background, ala Evolution, it puts a "sending message box smack dab in 
the middle of my workspace with a progress bar indicating that it is 
dutifully fulfilling it's function. I'd rather not be bothered with this 
display... and have it backgrounded so I can get back to email. I've 
looked and don't find a way to disable the notification. Anyone know? 
Thanks in advance. The thing is annoying. Ric