Mail Size Report is a simple Thunderbird extension that displays the size of the currently attached files, before sending an email.
Mail Size Report is an open source add-on designed to work with Mozilla Thunderbird 3.0 - 3.1.*.
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".