[mailop] IPv6 addresses for Microsoft Office 365 hosted domains?

[Bernhard Schmidt]

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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