Greg White <[EMAIL PROTECTED]> wrote:
>You really have to try to make qmail relay. Possible sources of relay:
>
>1. control/rcpthosts empty.
>2. RELAYCLIENT set for all/wrong addresses in /etc/tcp.smtp[.cdb]
>(or wherever you keep that file) if using tcpserver
>3. RELAYCLIENT set for all addresses in /etc/hosts.allow if using inetd.
>4. An insecure .cgi script on your machine (not possible if not running
>a cgi-capable webserver on your mail host), and RELAYCLIENT set for
>localhost.
One more that's bitten me in the past is a catch-all that forwards to
a smart host. Since the message is coming from a trusted host, the
smart host honors the relay request.
E.g., spammer sends message to host A addressed to
"victim%hostc@hosta". Host A, running qmail, has no "victim%hostc"
user or alias, but does have a ~alias/.qmail-default that forwards
undeliverable mail to a Sendmail or PMDF "smart" host, host B.
Host B receives the message addressed to "victim%hostc@hostb". It
trusts host A, and implements the percent hack, so it relays the
message to victim@hostc.
The fix is to check for funny chars in addresses (%!@) before
forwarding to the smart host.
-Dave
