|I dont use thunderbird, but here is some guidance on how to modify the connection timeout settings:|
Increase mailnews.tcptimeout from its default value of 60 seconds to 300 seconds using Tools -> Options -> Advanced -> General -> Connection timeout. This preference is only available in 1.5 or later. (In 3.x versions the setting is accessible only through the Config Editor - Tools->Options->Advanced->General->Config Editor.)
Click on the Config Editor button in Tools -> Options -> Advanced -> General
Type mailnews.tcptimeout at Filter:
It should list the settings just for mailnews.tcptimeout.
Look in the Value column and double click on that number. What is the number?
It should display a "Enter Integer value" window .
Change the number to at least 300 and press the OK button
Verify the new value is listed in the Value column. The Status column should also change from "default" to "user set".
Test thunderbird with your attachment again.