Erratic Thunderbird

[Keith Powell]

Thunderbird will behave for many days, then it will have a spell of 
marking *all* the downloaded messages as Junk. When it has marked 
about 150 messages, it is rather laborious manually unmarking each 
one (except the ones I recognise as junk!).

Does anyone else have this problem? Is there a way of unmarking them 
all in one go rather than individually?

It was the same in Hoary and with Thunderbird in other distros. So 
it's not just a Breezy Thunderbird problem.

Many thanks for any advice.

Keith