Timeout on dual core
From MozillaZine Knowledge Base
Thunderbird 1.0.7 doesn't appear to have any problems running on a dual core CPU such as a AMD Athlon 64 X2, Intel Pentium D, or Intel Pentium Extreme Edition. Thunderbird 1.5.0 and 18.104.22.168, however, have a bug where your connection may occasionally or even constantly timeout if you're using a dual core CPU. This may occur for IMAP, SMTP, and POP3 server connections. The recommended way of fixing this issue is to upgrade to 22.214.171.124 or the latest 1.5.0.x release.
The first step is to confirm whether its a dual core specific problem or not.
If the problem still occurs download the nspr4.dll file and save it to the C:\Program Files\Mozilla Thunderbird directory, overwriting the existing file. This fix was added to Thunderbird 126.96.36.199 and later. It is recommended that you upgrade to the latest 1.5.0.x release as a permanent resolution to these timeout issues.
If you're uncomfortable installing the Thunderbird patch installing the AMD driver or using a seperate launcher is the most user friendly solution.