Temporary block of @canonical.com sending to @lists.ubuntu.com

[Erich Eickmeyer]

For what it's worth, I have it on good authority that Red Hat is having 
the same trouble on Fedora lists.

On 1/9/26 8:20 AM, Robie Basak wrote:
> [writing as one member of the Ubuntu Technical Board]
>
> There is currently a technical problem affecting those with
> @canonical.com addresses using mailing lists hosted at
> @lists.ubuntu.com. To mitigate the impact, I propose to temporarily
> block, at mailing list level, emails from @canonical.com reaching
> @lists.ubuntu.com at all. Even better if Canonical IS could please do
> this at MTA level.
>
> At the moment, my best understanding of the problem is:
>
> 1. @canonical.com sets a DMARC policy.
>
> 2. When a @lists.ubuntu.com mailing list distributes an email sent by
> someone with a @canonical.com address, those emails do not comply with
> the @canonical.com DMARC policy.
>
> 3. When the email infrastructure of a third party subscriber to a
> @lists.ubuntu.com mailing list receives such an email and enforces the
> sender's DMARC policy, the email is rejected. As far as I can tell, this
> includes all mailing list subscribers who use Gmail and Fastmail.
>
> 4. The mailing list handler at @lists.ubuntu.com handles the rejection
> by (eventually) unsubscribing third party subscribes that enforce
> @canonical.com's own DMARC policy.
>
> I understand that there is a Canonical IS ticket open (C192498) that was
> filed on 25 November and has the details but the problem still
> continues.
>
> As long as this continues, the mailing lists are effectively unusable
> since they are failing to redistribute emails to third party subscribers
> in two ways: 1) third party subscribers who enforce sender DMARC policy
> do not receive emails from @canonical.com senders when they enforce
> @canonical.com's DMARC policy; and 2) third party subscribers are
> getting their mailing list deliveries suspended or unsubscribed entirely
> and when this happens they stop receiving emails from any mailing list
> sender and not just @canonical.com senders.
>
> If we implement the block I suggest, the problem will be migitated such
> that only @canonical.com aliases are affected. Everyone else will be
> able to carry on as usual. @canonical.com senders are already
> effectively excluded from mailing list participation due to their
> problem DMARC policy, so this would be strictly better than the current
> situation. In addition, then the @canonical.com senders would receive
> direct feedback of their email non-deliveries, rather than the current
> situation where it seems they are not aware of the problem.
>
> I'm not aware that @ubuntu.com senders are causing any issue, except
> that they are still affected by delivery suspension or unsubscription
> when @canonical.com senders send to the list. If you are a mailing list
> participant at Canonical and you have an @ubuntu.com alias, I suggest
> that you use it to minimise damage, and you'd be able to continue using
> it even with this temporary mitigation in place.
>
> Ironically, this message might itself be undeliverable to many
> subscribers for the same unsubscription reason. Messages do end up in
> the mailing list archive though, and I'll ensure to point to the other
> technical board members out of band.
>
> If there are no viable alternatives presented, I'll take this action
> after a week or two for the mailing lists that I have permission to
> administrate on lists.ubuntu.com, and encourage others to do the same
> for other mailing lists also hosted there.
>
> This sounds drastic so I thought it appropriate to discuss before taking
> action, particularly since the problem is now months old. I don't think
> it's as drastic as it sounds though, considering that it would result in
> strictly better performance than the current situation.
>
> Thanks,
>
> Robie
>