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MAIL FROM:<>RFC821, section 3.6 says:
This notification message must be from the server-SMTP at this
host. Of course, server-SMTPs should not send notification
messages about problems with 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 relayed it is permissible to leave the reverse-path
null. A MAIL command with a null reverse-path appears as follows:
MAIL FROM:<>
RFC1123, section 5.2.9 says:
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.
(emphasis and links added by me).
Error messages (in general:
delivery status notifications)
are sent this way, so they must not be rejected.
Guess what? Some people can't read and they have a setting in their mail server (IMail 4.0+ for NT) that rejects those addresses. Why are people allowed to distribute (sell?) such software? (they probably take some other company as bad example...).
user@YOUR.DOMAIN
Next, someone from YOUR.DOMAIN sends an e-mail to that user at REMOTE.DOMAIN which gets forward to user@YOUR.DOMAIN That is, your server receives an e-mail with a local sender address and a local receiver address, which is relayed from a remote system (REMOTE.DOMAIN).
If you would reject those mails, the above scenario would break. Can you make sure that this scenario won't happen? If you can, you may take a look at a proposal from Ted Deppner. However, you have to change it for 8.9.
Other proposals what should be in this text? Send me an e-mail. Thanks.