> How is it that this (weird, sort-of-null) From: address is whitelisted?
> It's surely not listed in my local.cf or user_prefs. Any ideas?
>From RFC 2821:
--------------------------------
If an SMTP server has accepted the task of relaying the mail and
later finds that the destination is incorrect or that the mail cannot
be delivered for some other reason, then it MUST construct an
"undeliverable mail" notification message and send it to the
originator of the undeliverable mail (as indicated by the reverse-
path). Formats specified for non-delivery reports by other standards
(see, for example, [24, 25]) SHOULD be used if possible.
This notification message must be from the SMTP server at the relay
host or the host that first determines that delivery cannot be
accomplished. Of course, SMTP servers MUST NOT send notification
messages about problems transporting notification messages. One way
to prevent loops in error reporting is to specify a null reverse-path
in the MAIL command of a notification message. When such a message
is transmitted the reverse-path MUST be set to null (see section
4.5.5 for additional discussion). A MAIL command with a null
reverse-path appears as follows:
MAIL FROM:<>
--------------------------------
Whether or not the null sender should be in the default whitelist is
subjective, but I think most would agree that it's prudent.
