Hi Frank, > > Thanks for sharing your experience. You may have been able to send > email to Google for some days from your IPv6 host without a PTR, but > I think that would only go on for a short time. Have you tried > sending to Comcast?
Note that I specifically do not suggest sending without PTR. We reject on missing FCrDNS even in IPv4 and are pretty happy with that (with an easy process to whitelist though). But I tried it to O365 and the mail went through nevertheless. According to https://www.m3aawg.org/sites/maawg/files/news/M3AAWG_Inbound_IPv6_Policy_Issues-2014-09.pdf which Google, Microsoft and LinkedIn claim to follow you need a "PTR and (SPF or DKIM)". And we've been preferring IPv6 outbound for 5+ years now, without any issues. 99% of our mail does neither have DKIM nor SPF. > From an ISP perspective, adding in an SPF (or equivalent TXT) record > for the IPv6 space of your ISP mail server would not be a hard thing > to do. While not all email servers support DKIM, all DNS servers > support TXT records. Both SPF and DKIM are controlled by the sender domain, not by the operator of the sending mailserver. Think the classic Permit-by-IP smarthost run by ISPs, you just cannot make any assumptions there about the sender. Bernhard
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