Re: [Exim] Matching bounce recipients against sender hashes

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Autor: Dennis Davis
Data:  
A: exim-users
Assumpte: Re: [Exim] Matching bounce recipients against sender hashes
>Cc: exim-users@???
>From: Tor Slettnes <tor@???>
>Subject: Re: [Exim] Matching bounce recipients against sender hashes
>To: Christian Balzer <chibi@???>
>Date: Fri, 11 Jun 2004 09:36:45 -0700


...

>I think I will send an e-mail to Evan Harris, suggesting that he:
>   - at some point in the future, consider writing up an RFC on
>greylisting;
>   - in that RFC, include a convention on including a unque ID in the
>envelope
>     sender, such as "<local_part>+<unique_id>@<domain>".


You need to be careful here, as email addresses of the above form
are used by some email systems. The MMDF mail system uses the "="
character instead of the "+" character for its own purposes. From
the manual page for maildelivery:


     MMDF treats local addresses which  contain  an  equals  sign
     ('=')  in  a  special manner.  Everything in a local address
     from an equals sign to the '@' is ignored and passed  on  to
     the  local  channel.  The local channel will make the entire
     string available for matching against the addr string of the
     .maildelivery  file.   For example, if you were to subscribe
     to a digest as "foo=digest@???", submit  and  the  local
     channel  will  verify  that it is legal to deliver to "foo",
     but then the entire string "foo=digest"  will  be  available
     for  string  matching against the .maildelivery file for the
     addr field.



I believe sendmail uses the "+" character for much the same purpose.

Problems may arise if exim is being used as a relay. You won't
necessarily know what systems you are delivering mail to, or
receiving mail from. There may be a good risk of confusion if
different systems are using the same operator (+) for totally
different purposes.