download managers for yahoo email?

I am kind of a newish person to macs-experienced in windows.....but no experience whatsoever in download managers in either platform. I know you can use a download manager to lessen your load on peak times.....
but can you do so in conjunction with email. We're running a small business from home and car.....and the comp internet is not a tax deduction yet.....but am asked to download absurdly large files. Is there a way to download the attachments while I am asleep?

juz left ur lappy and go to sleep... but make sure to that ur energy saver setting doesnt sleep the HD when u ar idle for certain time... for easiest way, user never for the sleep status...