SpamSieve does not have a feature to “bounce” spam messages back to the sender,
e.g. by sending an e-mail reply saying that the message was not delivered. Apple
Mail used to have a built-in Message ‣ Bounce command, but Apple has removed
it.
The thought behind bouncing is that a spammer will stop sending to your address
if he thinks that the address was invalid and his message didn’t get through.
Unfortunately, sending a “bounce message” back would be ineffective or even
counter productive for a variety of reasons:
- Spammers probably don’t care. They have lists of thousands or millions
of e-mail addresses, and it’s cheap to keep sending messages to the
entire list. They may get paid based on the size of their list, no matter
whether all the addresses are valid. In any case, it wouldn’t be worth
the effort to prune it down.
- You can’t contact them. Even if you believe that spammers care, your
bounce message probably wouldn’t get to them. Spammers use hijacked
machines and forged return addresses, so if you reply to a spam message
you’re likely sending your bounce to an invalid address or to an innocent
bystander.
- If you could, it might be bad for you. There is a narrow window of time
in which rejecting a spam message might work. When the mail server is in
the process of receiving a message, it’s talking to the sending server,
and so theoretically it could communicate that the address is invalid. By
the time the message has been delivered to your account, downloaded by
the mail program on your Mac, and filtered by SpamSieve, this window has
long since closed. At this point, if the spammer were listening, he’d
already know that the message had been delivered. If you were able to get
a bounce back to him, he’d know that it was a fake bounce. The original
message must have gotten all through, so he should send you more spam.
Since bouncing doesn’t work, it would be a waste of your time and network
resources to do it. Including such a feature in SpamSieve would falsely imply
that it should be used.