IPv6 Anti-spam nightmare

People are worried that IPv6 might create an anti-spam nightmare because IP-based blacklist systems will not be effective.  In IPv6 environment,  in a subnet, there are 2^64 IPv6 addresses to use.  Spammers can change their IPv6 addresses every single second or send out each spam mail with a different address.  With this uncertainty, some even say that there is no need to rush to implement IPv6 SMTP server as long as they have IPv4 SMTP servers to serve their corporate email communications.

This is a short-sighted view.  There are at least 2 methods I can think to circumvent IPv6 spamming hosts  which can change addresses frequently:

1.  Mandatory reverse lookup - unlike legitimate mail server, the random changing addresses of spamming hosts will not have proper reverse lookup records,

2.  Greylisting - spamming hosts will not queue up mail for subsequent retry but legitimate email servers perform this function.

Of course, above all, there is the solution of content filtering.  This method is more expensive as it requires the use of more CPU power, memory and a monthly subscription fee to obtain the database of spam signatures.