Thus, there are three possible scenarios:.
> 1) The mail came to my _server_ from a legitimate, full-blown,
> mail-server that knows the 'true identity' of the sender,
> regardless of what the "from" line says.
> 2) The mail cam to my
> server from dedicated spam-sending software that *doesn't* do
> _anything_ with rejection notices.
> 3) The message came to my server from a legitimate, full-blown,
> mail-server that does *not* know the identity of the sender.
Robert ... thanks for that explanation!
I'm a big fan of RBL blacklisting at the server, instead of filtering after delivery, for a number of reasons. This is one more reason I hadn't thought about: a better opportunity for a reasonable decision about whether to notify the (alleged) "sender" of the spam.
I used to rant against "silent" blocking. I thought ALL email should be either delivered or returned to the sender, or at least an attempt should be made to return it. I thought it was very bad that legitimate email could be silently tossed with neither the sender or the recipient being notified. If it was really spam, the bounce would probably go nowhere, but if it was good email, at least the sender would know he needed to find another way to contact the recipient.
Of course, as others have pointed out, this is a real problem now that spammers are forging valid return addresses. If the mail is filtered after delivery, the filter process can either throw it away or return it to an address which may be a real person who is not the source of the spam and doesn't need to be swamped with bounces from spam that he didn't send.
As Robert points out, if the delivery attempt is immediately rejected by the receiving server, it's up to the sending server to decide what to do about notification. In the case of legitimate mail, the sending server should be able to deliver a legitimate notification to the real sender. If it's spam, the sending server is probably not going to deliver a rejection notice to anybody, unless it's an open relay, and I think those are getting scarce. It seems that most spam these days is being blasted out by special-purpose spamming software, often running on hijacked broadband customers' machines, and those machines aren't likely to generate rejection notices.
[TELECOM Digest Editor's Note: I still suggest returning undelivered email 'to the sender'. If some innocent person gets a jillion pieces of mail because *someone else forged his email address* then maybe that person will get angry enough to join the effort to try and clean up the net. Read my autoack sometime, it says if you sent the email, then thank you for writing; _if you did not send the email_ then welcome to the club the rest of us belong to. (or words to that effect.) PAT]