I agree, its a problem
I think the example given several posts ago, where an ISP limits which SMTP server a person can talk to, is a minor problem compared to anyone being able to spoof internal users to blast internal domains with garbage e-mail that can get around spam filters because of the source address. I think thats a minor problem because the percentage of ISPs that actually do that is probably very low and certainly none of my users have that issue. My users do have the issue of e-mails being sent in with spoofed internal addresses.
So that brings about this valid scenario, when you use auto-whitelist with spamassassin, and an e-mail gets spoofed with an internal address but the content is spam? Auto-whitelist automatically whitelists it because its an internal address of the sender. That stinks. Either you live with it or shut off auto-whitelisting in spamassassin all because of this Qmail issue.
I think at a minimum it should be an option that should be allowed via a checkbox in Plesk so the administrator has the ability to stop that if they want to.
Also someone else mentioned that they thought version 8 had this same behavior, I have confirmed it on version 7.5.3 and version 8.x.
I did a quick check though that seems to support this as normal behavior by all the major free email players:
yahoo = allows unauthed
joe@yahoo.com to
joe@yahoo.com
aol = inconclusive
google = allows unauthed
joe@google.com to
joe@google.com
hotmail = allows unauthed
fred@hotmail.com to
fred@hotmail.com
I still wish I had the ability to stop this normal behavior.
qmail-spp doesn't seem to help by the way, I have tried and it never "sees" any auth information from plesk even when sending from an e-mail client that is definately authing (tcpdump confirmed). The environment variables for auth never get set. If qmail-spp actually did see the authing a person could have a plugin check if its authed when the rcpt and mail addresses match.
I just did some further checking, qmail-spp never seems to invoke auth plugins. Looking at the qmail-spp page I see that there are several versions of an auth patch for it based on which version of the qmail auth patch was implemented for qmail. They probably have patched qmail with qmail-spp only and not the qmail-spp-auth patch. If I had this, it would be easy to write a plugin that checked the sender, receiver--if both are local, make sure that the user auth'd. This is true for 7.5.3 I have not tested it on 8.0.1 yet.