How can a flag mail from specific mail relays as spam

[BB]

Recently had discussions about secondary mail server giving us the
most spam.  Some of it still gets through sa filters.

Would actually like to create our own secondary and setup as tarpit as
no valid mail should be sent to them if primary is up.

Before doing the above, is there a way to flag mail coming from the
secondary as spam ?

Doesn't blacklisting from only apply to the sender domain  and not the
relays between ?

Thanks

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