Most spam-mails with wrong sender
use domains like hotmail or other great freemailers. And this
freemailers doesn't use dynamic IPs. A test on this domains will
reject much more than 50% of spam...
spam keeps changing. block one way of sending spam and there will be
others. as long as it's cheap/easy to get an Internet account, spammers
will get throwaway accounts.
that and being able to send mail from multiple accounts with the same
return address is quite useful.
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