Bocking IP's rather than Email domains

[CodeHeads]

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Hello all,
Have a question:
Would it be better to block IP's instead of domains for an email server?

I guess would be that the person can change the domain in their reply
email address, so blocking IP ranges would be better, wouldn't it??

Example:
IP range = 222.168.0.0 - 222.169.255.255 (Actual spammer IP)

Wouldn't be better to place the IP's in iptables?? Or would another option
be better?

I hope this was not discussed at a later date. Just curious on what the IT
fields thinks of this. :)

- --
Best regards,
~WILL~
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