On 9/22/2014 10:41 AM, Wietse Venema wrote:
> This time PLEASE refrain from sidetracking the discussion. I want
> to know what will break when the default changes, if that is not
> too much to ask for.
>
> Summary:
>
> Until now, Postfix has a default setting "append_dot_mydomain = yes".
> This performs autocompletion from user@host to user@host.$mydomain.
> But this default setting is becoming problematic.
>
> I need to find out what will break when the default is changed to "no".
>
> How many people expect that this change would be a problem? It *may*
> affect mail that is submitted with the sendmail command line, or
> aliases that expand to user@host instead of user@host.domain. Email
> addresses in SMTP *should* already be fully qualified. But I also
> know that the real world often does not behave as it *should*.
> Hence this query to the postfix-users list.
>
> Details:
>
> Why is the default "append_dot_mydomain = yes", anyway?
>
> - It can be "convenient" to send mail to "user@host" and to have
> Postfix auto-complete the address to "user@host.$mydomain", or
> to specify aliases to "user@host" instead of "user@host.domain".
> Laziness is the primary reason append_dot_mydomain exists.
>
> Why change the append_dot_mydomain default to "no"?
>
> - The problem is that the current defauly produces incorrect results
> *with Postfix default settings*, meaning it is my fault, I can't
> blame the user, therefore something in Postfix needs to be changed
> to fix this (and not just adding warnings to documentation).
>
> Specifically, when the hostname is a registered domain such as
> example.com or example.ac.uk, Postfix default settings will
> auto-complete "user@localhost" to "u...@localhost.com" or
> "u...@localhost.ac.uk". Both forms are clearly bogus.
>
> - Some distributions already ship with "append_dot_mydomain = no".
> This is an opportunity to eliminate the inconsistency.
>
> Now, Postfix could know that it should not use a single label (".com"
> etc.) as the default mydomain value, but there are two-label domains
> like ".ac.uk" and even three-label ones that are equally inappropriate
> (though I think that their number is much smaller than the number
> of single-level names such as ".com", ".nl", etc.). So avoiding
> single-label suffixes (".com" etc.) is not perfect, but it may still
> be useful as a safety net.
>
> The real fix is not to auto-complete email addresses. That requires
> changing the default to "append_dot_mydomain = no". If people decide
> to change this to "yes", then I can blame them for not reading the
> warnings in the documentation :-)
>
> Wietse
>
My vote: Change the default and warn of the incompatible change in
the release notes. Maybe suggest adding the unqualified hostname to
mydestination in the notes?
Don't bother with a main.cf compatibility shim.
My thought: there are popular distros that have set this explicitly
to "no" for years, and yet we get very few questions here where the
artificial "no" setting causes a problem. So in a sense it's already
been tested for us.
-- Noel Jones
