In your letter dated 13 Mar 2017 18:43:21 +0100 you wrote: >Nor is gmail, which also requires that incoming IPv6 mail be authenticated >with SPF or DKIM. They know what they are doing, and they have decided >that the amount of legit mail they will lose by doing this is >insignificant compared to the improvement in the amount of spam and >malware they will be able to filter. That's not correct, unless gmail made an exception for my home mail server. Getting mail delivered to gmail over IPv6 works most of the time without ever setting up SPF or DKIM. Gmail does seem to be the single most unreliable mail server that I know of, mostly due to their attempts to be more strict on IPv6. What gmail does require is reverse DNS for IPv6.