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Re: special characters in mail address

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  • Viktor Dukhovni
    ... The RFC only defines SMTP, not the whole email ecosystem. Sure mimsy!chris@umd.edu is a local address at umd.edu from the perspective of SMTP, but
    Message 1 of 17 , Jul 3, 2012
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      On Tue, Jul 03, 2012 at 12:48:58PM +0000, Dentzer, Daniel wrote:

      > > > Beware that ! is a site separator in UUCP addresses.
      > > >
      > > > Good information.
      > > >
      > > > Is there a way to turn this off?
      > >
      > > this makes absolutely no sense
      > > you have to keep in mind that EVERY mailserver involved for delivering a
      > > message (and that can be many hops) has to accept a address as valid
      > >
      > > so usually do not use special chars at all!
      >
      > Why does it makes no sense, these Characters are valid as written in RFC 3696:

      The RFC only defines SMTP, not the whole email ecosystem. Sure

      mimsy!chris@...

      is a local address at "umd.edu" from the perspective of SMTP, but (still!) the
      majority of non-border Sendmail and Postfix systems will treat these as UUCP
      addresses and become multi-hop open relays if the border MTA does not refuse
      to forward these. Hence Postfix correctly treats these as source routes by
      default.

      If your system consists of just your server and is not a border
      relay and either refuses incoming mail or delivers it locally, then:

      swap_bangpath = no

      will disable UUCP support and allow incoming "abc!de" local parts,
      but these will be treated with prejudice everywhere else, so RFC
      or no RFC this address is not useful. There are de-facto standards
      that should or must not be ignored.

      --
      Viktor.
    • Dentzer, Daniel
      ... After a bit searching, and the great comments of you all, it looks like -see text above- a general problem of Postfix (and other mailsystems). But on the
      Message 2 of 17 , Jul 3, 2012
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        > -----Original Message-----
        > From: owner-postfix-users@... [mailto:owner-postfix-users@...]
        > On Behalf Of Viktor Dukhovni
        > Sent: Tuesday, July 03, 2012 3:21 PM
        > To: postfix-users@...
        > Subject: Re: special characters in mail address
        >
        > On Tue, Jul 03, 2012 at 12:48:58PM +0000, Dentzer, Daniel wrote:
        >
        > > > > Beware that ! is a site separator in UUCP addresses.
        > > > >
        > > > > Good information.
        > > > >
        > > > > Is there a way to turn this off?
        > > >
        > > > this makes absolutely no sense
        > > > you have to keep in mind that EVERY mailserver involved for
        > > > delivering a message (and that can be many hops) has to accept a
        > > > address as valid
        > > >
        > > > so usually do not use special chars at all!
        > >
        > > Why does it makes no sense, these Characters are valid as written in RFC
        > 3696:
        >
        > The RFC only defines SMTP, not the whole email ecosystem. Sure
        >
        > mimsy!chris@...
        >
        > is a local address at "umd.edu" from the perspective of SMTP, but (still!) the
        > majority of non-border Sendmail and Postfix systems will treat these as UUCP
        > addresses and become multi-hop open relays if the border MTA does not refuse
        > to forward these. Hence Postfix correctly treats these as source routes by
        > default.
        >
        > If your system consists of just your server and is not a border relay and
        > either refuses incoming mail or delivers it locally, then:
        >
        > swap_bangpath = no
        >
        > will disable UUCP support and allow incoming "abc!de" local parts, but these
        > will be treated with prejudice everywhere else, so RFC or no RFC this address
        > is not useful. There are de-facto standards that should or must not be
        > ignored.
        >
        > --
        > Viktor.


        After a bit searching, and the great comments of you all, it looks like -see text above- a general problem of Postfix (and other mailsystems). But on the other side, it is well known, that nobody should use unusual special characters.

        E.g. in http://en.wikipedia.org/wiki/Email_address#Specification are some more explanations:

        "Systems that send mail must be capable of handling outgoing mail for all valid addresses. Contrary to the relevant standards, some defective systems treat certain legitimate addresses as invalid and fail to handle mail to these addresses. Hotmail, for example, refuses to send mail to any address containing any of the following standards-permissible characters: !#$%*/?^`{|}~"

        But under Valid email addresses:
        !#$%&'*+-/=?^_`{}|~@...

        The result for me is, that I will persuade my company not to use most of the characters.


        Thank you all for the very fast and competent help.

        Daniel
      • Viktor Dukhovni
        ... The above text is unjustifiably pejorative. Systems that deal with the real world outside the standards group are not necessarily defective . Postfix is
        Message 3 of 17 , Jul 3, 2012
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          On Tue, Jul 03, 2012 at 01:26:37PM +0000, Dentzer, Daniel wrote:

          > E.g. in http://en.wikipedia.org/wiki/Email_address#Specification are some more explanations:
          >
          > "Systems that send mail must be capable of handling outgoing mail
          > for all valid addresses. Contrary to the relevant standards, some
          > defective systems treat certain legitimate addresses as invalid
          > and fail to handle mail to these addresses.

          The above text is unjustifiably pejorative. Systems that deal with the
          real world outside the standards group are not necessarily "defective".

          Postfix is quite capable of handling all the allowed RFC 2821/2822
          non-special characters in address localparts. By default, sensible
          security precautions and backwards compatibility settings are in
          place:

          - swap_bangpath = yes

          This protects internal systems (Sendmail, Postfix or other)
          from becoming multi-hop open relays if they support "host!user"
          UUCP address rewriting.

          - allow_percent_hack = yes

          Much the same, but for "user%internal@external" legacy addresses.

          - allow_min_user = no

          Protects careless administrators and shell script authors from their
          own folly. For example in master.cf pipe(8) argv= specs:

          SAFE:
          argv=myscript -f ${sender} -- ${recipient}
          UNSAFE:
          argv=myscript -f${sender} ${recipient}
          argv= argv=myscript -f ${sender} ${recipient}
          null_sender= argv=myscript -f${sender} -- ${recipient}

          Disable these measures at your peril. If your installation is simple
          and carefully maintained these are not needed. In practice people
          are lazy and sloppy and benefit from the extra care that Postfix
          takes to save them from themselves.

          --
          Viktor.
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