> Le 29/06/2026 à 09:11, Viktor Dukhovni via mailop a écrit :
> > On Mon, Jun 29, 2026 at 08:25:43AM +0200, Tobi via mailop wrote:
> >
> >> in the last days we're seeing that Microsoft is using
> >> "forms.mail.microsoft" as envelope SMTP sender-domain. As this domain
> >> does neither have A or MX it's considered unresolvable by our postfix
> >> MTA. Anyone else seeing that domain in their mailflow?
> >
> > Perhaps the MX RRset is newer than the messaegs you recorded, or perhaps
> > there's a DNS issue on your end.
>
> Another possibility
>
> Toby, are you on an IPv6 only network ?
It shouldn't matter whether the DNS resolver is on an IPv6-only (or
IPv4-only) network, because DNS will carry through A and AAAA records
regardless of that.
What does matter is that a resolver that doesn't have IPv4 won't be
able to query a remote nameserver that's IPv4-only (unless a
transition is handled somewhere in between, such as with an
IPv6-to-IPv4 gateway/proxy, etc.).
> I can see on Zonemaster that Microsoft's NS for `mail.microsoft.` does
> not respond to IPv6 queries
> https://zonemaster.net/en/result/3942ad544f4c9a1e/
Our DNS servers are resolving A and AAAA records for
mail.microsoft.com, but no MX records, so Postfix should fallback to
directly connecting to the IP addresses when attempting to deliver
mail to them.
> Same goes for `cloud.microsoft.`
> https://zonemaster.net/en/result/f97b652ebbe9fb52/
Our DNS servers are resolving multiple A and multiple AAAA records
for cloud.microsoft.com, but no MX records.
> --
> Grégory Rocher
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--
Postmaster - [email protected]
Randolf Richardson, CNA - [email protected]
Inter-Corporate Computer & Network Services, Inc.
Vancouver, Beautiful British Columbia, Canada
https://www.inter-corporate.com/
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