What is the root cause of IP in SpamCop list ?

As posted in the ClientNet Service Alerts, there have been several cases where a Symantec IP address is in the SpamCop list.  

We have had quite a few internal support cases,  because email is rejected when people send email to partners that use SpamCop.

Is there a "root cause"  that explains why this is occuring so often recently ?

What steps can be taken to reduce this problem ?

It is a real problem for us.

Thanks

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