[X4U] Apple Mail problem

[Murray E. Milligan]

I am using OS X 10.5.8.

I also use Mail 3.6

I've noticed quite a lot lately when I leave my mail program running  
in the background, I start to receive these annoying windows popping  
up telling me to
insert my password for my account. I cancel this window, then instruct  
mail to go back online and download my mail which it dows.

What gives with this? It happened before with 10.4, but now it's  
happening again.

Any quick cures that anyone knows about?

Murray