Email Synchronization?

I am using outlook 2003, I am sending and receiving email through yahoo.com
and my provider is bellsouth.net. I am able to send emails when in outlook
that are sent from yahoo I am unable to receive the emails that are going to
my yahoo account. I am sure that I have not set something up properly to
receive the emails in outlook from/through yahoo...sorry to be so long winded.
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Rick