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Subject: Re: null reverse-path
From: Rask Ingemann Lambertsen (rask-postfixkampsax.k-net.dk)
Date: Fri Jul 28 2000 - 18:17:11 CDT

Den 03-Jul-00 08:52:31 skrev adi fĝlgende om "Re: null reverse-path":

>How about receiving mail with null reverse-path with _many_ envelope
>recipients? Do we _must_ receive that kind of mail? I don't think
>so. I believe that there are some other ways to combat this kind of
>email, but that's not my point.

   As mentioned previously, it follows from RFC 1123 section 5.2.9 and RFC
821 example 7 and section 4.5.3 that you _must_ support at least 100 RCPT
commands, including the case where you get MAIL FROM:<>. Further, RFC 2505
section 2.6.1 specifically addresses this case, saying that it must be
supported:

-----
2.6.1. "MAIL From: <>"

   The MTA MUST NOT refuse to receive "MAIL From: <>".

   The "MAIL From: <>" address is used in error messages from the mail
   system itself, e.g. when a legitimate mail relay is used and forwards
   an error message back to the user. Refusing to receive such mail
   means that users may not be notified of errors in their outgong mail,
   e.g. "User unknown", which will no doubt wreak more havoc to the
   mail community than spam does.

   The most common case of such legitimate "MAIL From: <>" is to one
   recipient, i.e. an error message returned to one single individual.
   Since spammers have used "MAIL From: <>" to send to many recipients,
   it is tempting to either reject such mail completely or to reject all
   but the first recipient. However, there are legitimate causes for an
   error mail to go to multiple recipients, e.g. a list with several
   list owners, all located at the same remote site, and thus the MTA
   MUST NOT refuse "MAIL From: <>" even in this case.

   However, the MTA MAY throttle down the TCP connection ("read()"
   frequency) if there are more than one "RCPT To:" and that way slow
   down spammers using "MAIL From: <>".
-----

Regards,

/ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻTŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ\
| Rask Ingemann Lambertsen | E-mail: mailto:raskkampsax.k-net.dk |
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|To err is human. To forgive is beyond the scope of the Operating System.|