secondary mx? yes or no?

[Joe D'Andrea]

OK... for as long as I can remember we always configured our domains 
with primary and secondary MX servers. Then we got hit with spammers 
sending mail to our secondary and eventually our secondary became 
useless. The reason it became useless was because the primary, 
recognizing a large amount of non-deliverable mail (non-existant 
accounts that the secondary accepted) coming from the secondary would 
actually block the IP of the secondary for some period of time. If I 
could put the secondary in some whitelist somewhere that should 
eliminate its IP from being blocked. But do I really want all that 
mail being accepted by the secondary only to be discarded by the 
primary? What's the solution for this situation?

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