Chris Linfoot | DUMB: Mailing lists that spoof the the intended recpient's address as the sender

Friday, 29. August 2003

DUMB: Mailing lists that spoof the the intended recpient's address as the sender

Time for today's pet peeve.

MTA log today is full of:

29/08/2003 10:41:04 SMTP Server [05E8:0012-03F0] Mail from user@mydomain rejected for policy reasons. Sender is denied in your configuration.
29/08/2003 10:41:06 SMTP Server: listserv.example.com (192.168.0.1) disconnected. 0 message[s] received

[no names, no packdrill]

Turns out that the operator of a properly confirmed opt-in list used by a number of users here has taken to spoofing the intended recipients' addresses as the sender address. Of course, we do not accept any mail where the apparent sender is local. There is no legitimate reason why a remote sender would claim to be local. That is a spammer's trick.

The messages do eventually get through:

list server sends email to user@mydomain, "from" user@mydomain
we reject the mail (554 policy violation)
remote MTA generates a DSN to notify the apparent sender of the original mail that it could not be delivered
apparent sender is in fact the intended recipient, so we accept the DSN (MAIL FROM:<>) and deliver it to user@mydomain telling him that the mail he sent to himself could not be delivered, so here it is back again

Is it just me, or was that more difficult than it should have been?

Category: Dumb and Dumber
Technorati: Dumb and Dumber