dovecot - Apr 2021 - How to prevent, or change priority, of dovecot's FAILed relay-submission to relay's IPv6 address, and submit ONLY/first to IPv4?

On 4/9/21 12:55 PM, @lbutlr wrote:
> On 09 Apr 2021, at 08:29, PGNet Dev <pgnet.dev at gmail.com> wrote:
>>
>>>> And it's a bad assumption that since the host is dual-stack
that all services on it will be.
>>> If a hostname resolves to both an A and AAAA record, it should
provides services on both.
>>
>> Says who/what?
>>
>> There is no should/must/shall in any internet standard that
suggest/implies/requires that.
> 
> It's blatantly obnvisou because otherwise you have to try to figure out
if www.example.com:587 is on the A or the AAAA record, which is pretty much he
opposite of how multiple records work.

er, huh?

the 'net doesn't run on what you think is 'blatantly obvious'. 
at least _my_ 'net doesn't.

just because there's an available record does not mean that one intends to,
let alone HAS to, use it.

If you want to manage your infrastructure to suit your needs, then do so. 
That's the point.  It's your choice.  Feel free to be as loose or locked
down as you choose.

Postfix, as well as other services, seems to manage this all quite nicely. 
Define/restrict listeners as needed.

Postfix, e.g., diligently adheres to internet standards, typically making them
defaults, and often-not-always providing a knob to override.
Where a standard does not mandate a preference, the preference is available
& configurable by default.
The app does not presume to assume what your infrastructure should be. Or other
silly assumptions for that matter.

OTOH, Re: this^ IPv6 business, dovecot,

- *hardcodes* the order of inet addr family preference -- IPv6 first -- in its
source
- ignores system-defined precedence of IPv6/IPv4 in /etc/gai.conf
- provides no option to set/override

There's no sound reason -- technical or otherwise -- of not providing
perfectly legitimate infrastructure-config choices to the admin, and an option
to override default behaviors.
Especially when the override is of defaults that are questionable,
internally-made assumptions in the 1st place.

On Fri, Apr 09, 2021 at 01:15:27PM -0400, PGNet Dev
wrote:
>There's no sound reason -- technical or otherwise -- of not providing
perfectly legitimate infrastructure-config choices to the admin, and an option
to override default behaviors.
>Especially when the override is of defaults that are questionable,
internally-made assumptions in the 1st place.
>
There most certainly is a sound reason, which is that it is code that would need
to be written and maintained in order to solve a problem that is at least
arguably user error.  If the admin specifies a name rather than an IP address,
and that name resolves to multiple addresses (whether they be different families
of address is irrelevant), then the software is entirely correct in deciding to
use any of those addresses in whatever order it wants.  If you want to route
around the DNS because of breakage in your local configuration, use a specific
address or create a name that contains only the addresses you want. It is
unreasonable instead to impose a burden of maintenance on the dovecot
developers, or the penalty of poorly-exercised code (since this is, frankly, a
corner case) on all the users.

Regards,

A
-- 
Andrew Sullivan
ajs at crankycanuck.ca