On Thu, 5 Nov 1998, Frank Elsner wrote:
> Nearly all hosts an the campus LAN and in the relay_domains have old
> sendmail configurations and refuse to accept error messages which
> have the empty sender <>.
This used to be quite common. Here is the text I sent to admins of such
systems that I come across:
Unfortunately, some users of sendmail have configurations that don't handle
this correctly. I suspect that the following line is missing from ruleset 3 of
your /etc/sendmail.cf file:
R<> $@@ return magic token
> I need a pointer where to modify exim to generate a non-empty sender,
> maybe "Mailer-Daemon@$primary_hostname".
DON'T do this. It is againt all the RFCs. The reason for empty senders
in bounce messages is to guard against bounce loops. Here's the quote
from RFC 1123:
5.2.9 Command Syntax: RFC-821 Section 4.1.2
The syntax shown in RFC-821 for the MAIL FROM: command omits
the case of an empty path: "MAIL FROM: <>" (see RFC-821 Page
15). An empty reverse path MUST be supported.
[...]
5.3.3 Reliable Mail Receipt
When the receiver-SMTP accepts a piece of mail (by sending a
"250 OK" message in response to DATA), it is accepting
responsibility for delivering or relaying the message. It must
take this responsibility seriously, i.e., it MUST NOT lose the
message for frivolous reasons, e.g., because the host later
crashes or because of a predictable resource shortage.
If there is a delivery failure after acceptance of a message,
the receiver-SMTP MUST formulate and mail a notification
message. This notification MUST be sent using a null ("<>")
reverse path in the envelope; see Section 3.6 of RFC-821. The
recipient of this notification SHOULD be the address from the
envelope return path (or the Return-Path: line). However, if
this address is null ("<>"), the receiver-SMTP MUST NOT send a
notification. If the address is an explicit source route, it
SHOULD be stripped down to its final hop.
This is one issue where I really feel that I should not encourage you to
modify Exim.
And should you have admitted in a public forum that your hosts are
running old versions of Sendmail? I hope it doesn't encourage anyone to
start attacking them.
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
--
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