Two problems really:
I'm using Mac Mail version 5.3 on Mac OSX. My Yahoo mailbox is continually fetching new mail i.e. the wheel by 'yahoo is continually spinning. It has been doing this for a few days. I have already tried quitting and reopening Mac mail a few times.
I can see see from Window>Activity that Yahoo inbox is caching attachments. Even if I stop it, it starts again within seconds.