What does IPv6 mean for delivery?
IPv4 allows for around 4 billion addresses, of which 3.7 billion are usable. This address space is becoming increasingly exhausted. At the end of July 2015 only 160,000 IPv4 addresses were still available to the American Registry for Internet Numbers (ARIN): That represents 0.01% of the total addresses managed by ARIN. IPv6 is a must in order to continue to be able to address the growing number of servers in future.