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From: Timo Sirainen on 7 Mar 2010 18:54
On 8.3.2010, at 1.26, Wietse Venema wrote:

> smtp_address_preference (default: ipv6)

Probably the whole reason for this thread was because of me. I used to have a working IPv6 setup, and then switched to a different ISP and just copied all my configs. Everything worked fine for a few days so I didn't think too much about it after that. Then several years later I hear Erik's having problems subscribing to Dovecot mailing list.

Of course I fixed the problem immediately as I found out about it, but I'm just wondering how many other such setups there are that break once IPv6 becomes more common. Should this setting default to "any"? Is there really even a reason for it to be other than "any" (at least until IPv6 really is commonly used everywhere)?

From: Wietse Venema on 7 Mar 2010 19:22
Timo Sirainen:
> On 8.3.2010, at 1.26, Wietse Venema wrote:
>
> > smtp_address_preference (default: ipv6)
>
> Probably the whole reason for this thread was because of me. I
> used to have a working IPv6 setup, and then switched to a different
> ISP and just copied all my configs. Everything worked fine for a
> few days so I didn't think too much about it after that. Then
> several years later I hear Erik's having problems subscribing to
> Dovecot mailing list.
>
> Of course I fixed the problem immediately as I found out about
> it, but I'm just wondering how many other such setups there are
> that break once IPv6 becomes more common. Should this setting
> default to "any"? Is there really even a reason for it to be other
> than "any" (at least until IPv6 really is commonly used everywhere)?

Perhaps, that's why I talked about "smtp_address_preference = any"
on the mailing list.

Currently, Postfix ships with "inet_protocols = ipv4" as the default,
so people who turn on IPv6 support should know what they are doing.

I don't know common it is to have different performance levels or
different failure modes for IPv6 and IPv4. Nor do I know how common
it is for destinations to have half a dozen or more IPv6 addresses
(i.e. more than the default Postfix smtp_mx_address_limit of 5).

Wietse

From: Timo Sirainen on 7 Mar 2010 19:44
On 8.3.2010, at 2.22, Wietse Venema wrote:

>> Of course I fixed the problem immediately as I found out about
>> it, but I'm just wondering how many other such setups there are
>> that break once IPv6 becomes more common. Should this setting
>> default to "any"? Is there really even a reason for it to be other
>> than "any" (at least until IPv6 really is commonly used everywhere)?
>
> Perhaps, that's why I talked about "smtp_address_preference = any"
> on the mailing list.

Yeah, just trying to give some example.

> Currently, Postfix ships with "inet_protocols = ipv4" as the default,
> so people who turn on IPv6 support should know what they are doing.

And when I changed it, I did know what I was doing. But a few years later I forgot about it. When switching ISP, it was obvious that I had to change my IP addresses, so I changed them in all my configs. But it was much less obvious that I had to change anything else, like remember that I had enabled IPv6 in some application that could sometimes break because of that change. That brings another thought to my mind: Maybe the default could be based on current DNS settings? If the server's primary address has IPv6 DNS record, prefer it, otherwise prefer any. (I haven't thought much yet if it's that good of an idea.)

> I don't know common it is to have different performance levels or
> different failure modes for IPv6 and IPv4. Nor do I know how common
> it is for destinations to have half a dozen or more IPv6 addresses
> (i.e. more than the default Postfix smtp_mx_address_limit of 5).

Me neither. And it was fine for many years. But maybe it's soon getting worse as IPv4 address availability is disappearing.
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