A study conducted by RIPE Labs indicates that about 1.89% of spam are received over IPv6.
"With the increased deployment of IPv6, we were curious to see how much the amount of spam sent over IPv6 increases. We looked at the e-mail system of the RIPE NCC and produced some statistics that could be seen as an indication for the overall trend of spam sent over IPv6," says RIPE in a blog post explaining the analysis. Group also notes that the study was based on one week’s worth of data and that it excluded messages already rejected by blacklisting and greylisting.
RIPE Labs: Spam over IPv6