In addition to sending bounce messages with a non-null reverse path, I have also discovered that Fetchmail invents a from address for bounce messages received with a null reverse path, consisting of <username>@<POP3 servername>, which in my case is not a valid address.
If a spam is forged as coming from a non-existent address on my machine, and bounces, Fetchmail will receive the bounce, find it can't deliver it and send a new bounce message to the from address it has just invented. This in turn will also bounce. The only reason I haven't had mail loops is because I added a mail alias for FETCHMAIL-DAEMON, so that bounces which bounce back to that address don't themselves generate new bounces. An example is shown below. Using the SDPS protocol, the *ENV command is used to obtain the envelope to and from addresses. This is documented at http://www.demon.net/helpdesk/producthelp/mail/sdps-tech.html/ I haven't been able to force Fetchmail to use standard POP3 as the protocol option appears to be ignored. fetchmail: starting fetchmail 6.2.5 daemon fetchmail: 6.2.5 querying pop3.demon.co.uk (protocol POP3) at Fri 22 Jul 2005 17:30:13 BST: poll started fetchmail: POP3< +OK demon POP3 server ready (demon.co.uk) fetchmail: POP3> USER rilynn fetchmail: POP3< +OK fetchmail: POP3> PASS * fetchmail: POP3< +OK fetchmail: selecting or re-polling default folder fetchmail: POP3> STAT fetchmail: POP3< +OK 1 2153 fetchmail: 1 message for rilynn at pop3.demon.co.uk (2153 octets). fetchmail: POP3> LIST 1 fetchmail: POP3< +OK 1 2153 fetchmail: POP3> *ENV 1 fetchmail: POP3< +OK fetchmail: POP3< ok fetchmail: POP3< rilynn.demon.co.uk fetchmail: POP3< *** The line above is the envelope from address. Below is the envelope to address. *** fetchmail: POP3< [EMAIL PROTECTED] fetchmail: POP3< . fetchmail: POP3> RETR 1 fetchmail: POP3< +OK fetchmail: reading message [EMAIL PROTECTED]:1 of 1 (2153 octets) fetchmail: passed through [EMAIL PROTECTED] matching rilynn.demon.co.uk fetchmail: SMTP< 220 rilynn.demon.co.uk ESMTP Exim 4.50 Fri, 22 Jul 2005 17:30:17 +0100 fetchmail: SMTP> EHLO localhost fetchmail: SMTP< 250-rilynn.demon.co.uk Hello localhost [127.0.0.1] fetchmail: SMTP< 250-SIZE 52428800 fetchmail: SMTP< 250-PIPELINING fetchmail: SMTP< 250 HELP fetchmail: forwarding to localhost fetchmail: SMTP> MAIL FROM:<[EMAIL PROTECTED]> SIZE=2153 *** Above Fetchmail has invented an invalid envelope from address, which is where any Delivery Status Notifications will be sent. *** fetchmail: SMTP< 250 OK fetchmail: SMTP> RCPT TO:<[EMAIL PROTECTED]> fetchmail: SMTP< 250 Accepted The Return-path: header, obtained by telnetting to the POP3 server is: Return-path: <> By the time it has arrived in my mailbox this has become: Return-path: [EMAIL PROTECTED] Regards, Roger -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]