For the past 3 days, my Thunderbird has not been able to download mail. It would just sit there trying to download the first email.

I tried selectively disabling 1 pop account at a time, disabling AV scanning, moving my profile from one disk to another - none of it worked. I also read through a few pages of threads in the official Thunderbird forums too - no issues seem to match mine..

Then I decided to disable all the message filters - wollah! fixed..

So lesson learnt - if Thunderbird is causing you grief for no particular reason - try disable your filters..

I seem to have been able to re-enable them now, and it works ok.. damn random thunderbird issues!