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Re: Multiple recipient_delimiter address extensions?

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  • Wietse Venema
    ... It would be relatively easy to implement truncate the localpart at the first instance of any character in the delimiter set, then do one table lookup
    Message 1 of 16 , Apr 4, 2013
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      Kris Deugau:
      > grarpamp wrote:
      > > I've done - (qmail) to + (postfix) hurriedly in the past to avoid a
      > > meta issue. Other users migration or dual uses aside, with that
      > > one I wanted to but did not have benefit to research whether
      > > + or - had better merits. Such as which is in more common use now,
      > > which is trending to be more prevalent in the long term. And why?
      > > Honestly, best I could come up with was the large - legacy from
      > > decade old qmail-like installations, and not requiring the shift key
      > > seemed to win, heh :) I'm sure there are more sound thoughts
      > > on the matter in a paper somewhere.
      >
      > - has the fairly significant advantage of being allowed on more sites
      > that try to validate "well-formed" email addresses - often in
      > Javascript. Many such validators reject + in an email address. :(

      It would be relatively easy to implement "truncate the localpart
      at the first instance of any character in the delimiter set, then
      do one table lookup" (basically, replacing strchr() with strcspn()).

      This would allow one to use '-' for some websites and '+' for others.

      This could later be made more configurable, for example "for each
      delimiter in the specified order: truncate the localpart, do
      table lookup, and stop after the first successful lookup".

      As long as users stick to names with [a-zA-Z0-9.], the first,
      simpler, implementation should be sufficient.

      Wietse
    • Wietse Venema
      ... Unfortunately this would break existing code that expands $recipient_delimiter, for example the forward_path default value. This means using a new
      Message 2 of 16 , Apr 4, 2013
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        Wietse Venema:
        > Kris Deugau:
        > > grarpamp wrote:
        > > > I've done - (qmail) to + (postfix) hurriedly in the past to avoid a
        > > > meta issue. Other users migration or dual uses aside, with that
        > > > one I wanted to but did not have benefit to research whether
        > > > + or - had better merits. Such as which is in more common use now,
        > > > which is trending to be more prevalent in the long term. And why?
        > > > Honestly, best I could come up with was the large - legacy from
        > > > decade old qmail-like installations, and not requiring the shift key
        > > > seemed to win, heh :) I'm sure there are more sound thoughts
        > > > on the matter in a paper somewhere.
        > >
        > > - has the fairly significant advantage of being allowed on more sites
        > > that try to validate "well-formed" email addresses - often in
        > > Javascript. Many such validators reject + in an email address. :(
        >
        > It would be relatively easy to implement "truncate the localpart
        > at the first instance of any character in the delimiter set, then
        > do one table lookup" (basically, replacing strchr() with strcspn()).
        >
        > This would allow one to use '-' for some websites and '+' for others.

        Unfortunately this would break existing code that expands
        $recipient_delimiter, for example the forward_path default value.

        This means using a new parameter name for the recipient delimiter
        set, and making the recipient_delimiter default value dependent on
        the value of that new parameter (for example take the first character).

        Wietse

        > This could later be made more configurable, for example "for each
        > delimiter in the specified order: truncate the localpart, do
        > table lookup, and stop after the first successful lookup".
        >
        > As long as users stick to names with [a-zA-Z0-9.], the first,
        > simpler, implementation should be sufficient.
        >
        > Wietse
        >
      • Wietse Venema
        I ve done a proof-of-concept implementation that works as documented below the signature. This retains the old recipient_delimiter parameter because that
        Message 3 of 16 , Apr 4, 2013
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          I've done a proof-of-concept implementation that works as documented
          below the signature.

          This retains the old recipient_delimiter parameter because that
          parameter has been in use since 19981029 in the forward_path default
          parameter value, and I can't have a multi-character value there.

          To support users that have .forward+foo and .forward-foo, you'd
          have to spell the file names explicitly:

          /etc/postfix/main.cf:
          recipient_delimiters = +-
          forward_path =
          $home/.forward+${extension},
          $home/.forward-${extension},
          $home/.forward

          This works regardless of what the delimiter in the email address
          was; Postfix does not use that when it searches forward_path.

          Wietse

          recipient_delimiters (default: $recipient_delimiter)
          The set of characters that can separate user names and
          address extensions (user+foo). See canonical(5),
          local(8), relocated(5) and virtual(5) for the effects
          this has on aliases, canonical, virtual, and relocated
          lookups. Basically, the software tries user+foo before
          trying user.

          When the recipient_delimiters set contains multiple
          characters, user names and address extensions are
          separated at the first character that matches the
          recipient_delimiters set. The implementation recognizes
          only one delimiter character per email address.

          By default, the recipient_delimiter (note: singular)
          value equals the first character of the recipient_delimiters
          parameter value. The recipient_delimiter parameter is
          used in the default forward_path value, where the
          software tries .forward+foo before trying .forward.

          When the recipient_delimiters parameter is not specified,
          its value defaults to the recipient_delimiter value.

          Example:

          # Handle both Postfix and qmail extensions.
          recipient_delimiters = +-
        • Wietse Venema
          ... I was able to simplify this further. The result is below. Comments are welcome. The problem with forward_path could be solved without requiring changes to
          Message 4 of 16 , Apr 5, 2013
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            Wietse Venema:
            > I've done a proof-of-concept implementation that works as documented
            > below the signature.

            I was able to simplify this further. The result is below.
            Comments are welcome.

            The problem with forward_path could be solved without requiring
            changes to the forward_path default setting:

            forward_path = $home/.forward${recipient_delimiter}${extension},
            $home/.forward

            When Postfix expands this while delivering mail, it now replaces
            ${recipient_delimiter} with the actual recipient delimiter in the
            recipient email address, instead of using the main.cf value.

            recipient_delimiter (default: empty)
            The set of characters that can separate user names and
            address extensions (user+foo). See canonical(5),
            local(8), relocated(5) and virtual(5) for the effects
            this has on aliases, canonical, virtual, and relocated
            lookups. Basically, the software tries user+foo before
            trying user.

            When the recipient_delimiter set contains more than one
            character (Postfix 2.11 and later), user names and
            address extensions are separated at the first character
            that matches the recipient_delimiter set. The
            implementation recognizes only one delimiter character
            per email address.

            When used in forward_path, ${recipient_delimiter} is
            replaced with the actual recipient delimiter in the
            recipient email address.

            Examples:

            # Support Postfix and qmail extensions (Postfix >= 2.11).
            recipient_delimiter = +-

            # Use .forward for mail without address extension, or
            # with an unrecognized address extension.
            forward_path = $home/.forward,
            $home/.forward${recipient_delimiter}${extension}

            This seems like a more reasonable implementation.

            Support for delimiter priorities could be added later but I doubt
            that it will really solve problems.

            Wietse
          • Viktor Dukhovni
            ... One issue this does not discuss is the handling of: propagate_unmatched_extensions = canonical, virtual a relay that accepts multiple extensions and
            Message 5 of 16 , Apr 5, 2013
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              On Fri, Apr 05, 2013 at 09:23:42AM -0400, Wietse Venema wrote:

              > Wietse Venema:
              > > I've done a proof-of-concept implementation that works as documented
              > > below the signature.
              >
              > I was able to simplify this further. The result is below.
              > Comments are welcome.

              One issue this does not discuss is the handling of:

              propagate_unmatched_extensions = canonical, virtual

              a relay that accepts multiple extensions and validates addresses
              via relay_recipient_maps, may forward mail via SMTP to downstream
              destinations which handle a subset (possibly none) of the supported
              extensions. This can create bouncebacks.

              Even with a single recipient delimiter (say "+"), I've had to set:

              propagate_unmatched_extensions = canonical

              so that envelope recipients forwarded to Microsoft Exchange were
              not extended, since Exchange does not support extensions.

              The general picture is more complex, since while MUAs only need
              extensions in headers to help users sort incoming mail, the delivery
              MTA (e.g. qmail or Postfix via forward_path, ...) uses the envelope
              recipient.

              So a complete implementation possibly needs to be able to determine
              the correct downstream recipient delimiter based on the destination
              nexthop or transport:nexthop. In recursive virtual (or canonical)
              expansion this logic need only apply to the final address.

              I'm also concerned that matching the first delimiter is problematic
              in mixed environments. When a relay sits in front of two domains
              example.com (whose extension is "+") and example.net (whose extension
              is "-") we don't get correct behaviour:

              postfix-users+extension@...
              user-extension+more-extension@...

              the relay would bounce the "postfix-users+extension" mail, as it
              would misinterpret this as being addressed to "postfix", unless in
              fact multiple lookups are made, and the recipient delimiter is
              inferred from the shortest match (try "postfix" - "...", then
              "postfix-users" + "...").

              If we do add support for destination specific address extensions
              on output, what should be done with the wrong extension on input?
              Hypothetical:

              postfix-users-mumble@...

              is just an invalid address when example.com is a "+" delimiter domain.

              So I'm not entirely convinced we're not opening up a bit of a can
              of worms.

              --
              Viktor.
            • /dev/rob0
              ... Thanks. A very minor complaint is that you have always been very consistent IIRC regarding plural and singular in parameter names, but now
              Message 6 of 16 , Apr 5, 2013
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                On Fri, Apr 05, 2013 at 09:23:42AM -0400, Wietse Venema wrote:
                > Wietse Venema:
                > > I've done a proof-of-concept implementation that works as
                > > documented below the signature.
                >
                > I was able to simplify this further. The result is below.
                > Comments are welcome.

                Thanks. A very minor complaint is that you have always been very
                consistent IIRC regarding plural and singular in parameter names, but
                now "recipient_delimiter" can be multiple characters. :) (I do
                understand why it works better in this case; just saying, maybe for
                naming consideration in a Postfix 3.0.)

                I will not be able to get to this until early next week, but at that
                time I'll upgrade and experiment with this.

                I really hated switching from + to - as delimiter. It felt like the
                wrong thing to do, accomodating some fool who happened to write a
                popular PHP library function. It will be nice to be positive again.
                :)
                --
                http://rob0.nodns4.us/ -- system administration and consulting
                Offlist GMX mail is seen only if "/dev/rob0" is in the Subject:
              • Wietse Venema
                ... First, lest I sound ungrateful later, thanks for the comments. ... This problem is old: it exists whether or not recipient_delimiter specifies a single
                Message 7 of 16 , Apr 5, 2013
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                  Viktor Dukhovni:
                  > On Fri, Apr 05, 2013 at 09:23:42AM -0400, Wietse Venema wrote:
                  >
                  > > Wietse Venema:
                  > > > I've done a proof-of-concept implementation that works as documented
                  > > > below the signature.
                  > >
                  > > I was able to simplify this further. The result is below.
                  > > Comments are welcome.

                  First, lest I sound ungrateful later, thanks for the comments.

                  > One issue this does not discuss is the handling of:
                  >
                  > propagate_unmatched_extensions = canonical, virtual
                  >
                  > a relay that accepts multiple extensions and validates addresses
                  > via relay_recipient_maps, may forward mail via SMTP to downstream
                  > destinations which handle a subset (possibly none) of the supported
                  > extensions. This can create bouncebacks.

                  This problem is old: it exists whether or not recipient_delimiter
                  specifies a single character or a set of characters.

                  > postfix-users+extension@...
                  > user-extension+more-extension@...

                  This problem is old, too: it exists whether or not recipient_delimiter
                  specifies a single character or a set of characters.

                  Note that an address extension exists only because the owner of the
                  email address decided to use that extension in the first place.

                  If the owner of an email address decides to use address extensions,
                  then she should choose a username that doesn't contain any of the
                  common user/extension delimiters.

                  Wietse
                • Wietse Venema
                  ... Yes and no. Postfix still supports only one user/extension separator per address. A feature name that contains the word delimiters would send the message
                  Message 8 of 16 , Apr 5, 2013
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                    /dev/rob0:
                    > On Fri, Apr 05, 2013 at 09:23:42AM -0400, Wietse Venema wrote:
                    > > Wietse Venema:
                    > > > I've done a proof-of-concept implementation that works as
                    > > > documented below the signature.
                    > >
                    > > I was able to simplify this further. The result is below.
                    > > Comments are welcome.
                    >
                    > Thanks. A very minor complaint is that you have always been very
                    > consistent IIRC regarding plural and singular in parameter names, but
                    > now "recipient_delimiter" can be multiple characters. :) (I do

                    Yes and no. Postfix still supports only one user/extension separator
                    per address.

                    A feature name that contains the word "delimiters" would send the
                    message that Postfix supports "multiple delimiters" within an address.

                    > I really hated switching from + to - as delimiter. It felt like the
                    > wrong thing to do, accomodating some fool who happened to write a
                    > popular PHP library function. It will be nice to be positive again.
                    > :)

                    I see some late revenge.

                    Wietse
                  • grarpamp
                    hi. i ve briefly reviewed some of this posted work and it seems reasonable. and refreshing to see work come from my simple query. so give the new option a go
                    Message 9 of 16 , Apr 10, 2013
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                      hi. i've briefly reviewed some of this posted work and it seems reasonable.
                      and refreshing to see work come from my simple query. so give the new
                      option a go as best seen fit! thanks.
                    • Jeroen Geilman
                      ... $recipient_delimiter_alternatives ? -- J.
                      Message 10 of 16 , Apr 11, 2013
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                        On 04/05/2013 08:17 PM, Wietse Venema wrote:
                        > /dev/rob0:
                        >>
                        >> Thanks. A very minor complaint is that you have always been very
                        >> consistent IIRC regarding plural and singular in parameter names, but
                        >> now "recipient_delimiter" can be multiple characters. :) (I do
                        > Yes and no. Postfix still supports only one user/extension separator
                        > per address.
                        >
                        > A feature name that contains the word "delimiters" would send the
                        > message that Postfix supports "multiple delimiters" within an address.

                        $recipient_delimiter_alternatives ?

                        --
                        J.
                      • Wietse Venema
                        ... That is better. After working through feature update, I noticed that the delimiter is also applied to sender addresses, so I am declined to replace the
                        Message 11 of 16 , Apr 11, 2013
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                          Jeroen Geilman:
                          > On 04/05/2013 08:17 PM, Wietse Venema wrote:
                          > > /dev/rob0:
                          > >>
                          > >> Thanks. A very minor complaint is that you have always been very
                          > >> consistent IIRC regarding plural and singular in parameter names, but
                          > >> now "recipient_delimiter" can be multiple characters. :) (I do
                          > > Yes and no. Postfix still supports only one user/extension separator
                          > > per address.
                          > >
                          > > A feature name that contains the word "delimiters" would send the
                          > > message that Postfix supports "multiple delimiters" within an address.
                          >
                          > $recipient_delimiter_alternatives ?

                          That is better. After working through feature update, I noticed
                          that the delimiter is also applied to sender addresses, so I am
                          declined to replace the recipient_ portion.

                          Perhaps this is a path into the future:

                          recipient_delimiter
                          This is no longer a main.cf parameter. It is used only in the
                          $forward_path, where it expands into the user/extension separator
                          that was found in the recipient email address.

                          address_delimiter_alternatives (default: $recipient_delimiter)
                          This is a new main.cf parameter, containing the set of characters
                          that may separate a user name from an address extension (user+foo)
                          in a sender or recipient address. The default setting maintains
                          backwards compatibility fo rexisting configurations.

                          Wietse
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