[PLUG] Relaying problem fixed...here's how

["Tom Joyce" <tgj@snip.net>]

Hi,
The past few days I was a victim of email relaying through my server.
I thought I would pass along what I found out and how I stopped it.

My installation is generally off the CD installation of Red Hat 6.1
I installed , from the Disk, Sendmail and used linuxconf to set some mail
defaults.
I later found out the linuxconf had some bugs one of which related to
configuring sendmail.

I ended up replacing the sendmail.cf file with the original one generated
from the first installation.
{I backed it up before I messed with it way back then} .
I added some specific comments relative to my system by hand to that file
and restarted sendmail.

The problem I found was related to the senmail.cf file and also the
following:

In my /etc/hosts file there is the line:
127.0.0.1       localhost       localhost.localdomain

In the /etc/mail/access file there was this:
# Check the /usr/doc/sendmail-8.9.3/README.cf file for a description
# of the format of this file. (search for access_db in that file)
# The /usr/doc/sendmail-8.9.3/README.cf is part of the sendmail-doc
# package.
#
# by default we allow relaying from localhost...
localhost.localdomain          RELAY
localhost                      RELAY

This was allowing relaying through my system.
I commented them out by putting the # before each line.
Ran the command:
makemap -v btree access < access

Restarted sendmail and it doesn't relay anymore.

Hope this may help someone else out.

Thanks out to http://www.orbs.org/ and also http://www.abuse.net/relay.html
They have links and services to help prevent relaying and spam in general.

Tom




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