Get before Send is a Thunderbird extension that allows you to get messages for the account which is bound to the identity then send the message.
Get messages for the account which is bound to the identity then send the message when you click the toolbar button or the menu item.
If your sever authenticates using "POP before SMTP", the extension is useful.
You can specify the account which is received in the extension's option from version 0.6.10. The SMTP server whose received account is set as "None" does not get messages before sending. I think you will not need the original send button by setting it appropriately :)
In order to use toolbar button, right-click on the toolbar and select "customize" then drag&drop the icon.
How to Install in Thunderbird:
1. Right-click the link below and choose "Save Link As..." to download and save the file to your hard disk.
2. In Mozilla Thunderbird, open Add-ons from the Tools menu.
3. Click the Install button, and locate/select the file you downloaded and click "OK".