5XX vs 4XX

[John Schmerold]

I have a few email addresses that were valid 15 years ago, but they have 
been invalid for 5+ years, we are rejecting them with a 450 message, my 
thought is "Let's tie up this spammer's computer just a little bit"

Good idea? Bad idea? Effective? Ineffective?
--
John Schmerold
Katy Computer Systems, Inc
https://katycomputer.com
St Louis