RE: Securing Sendmail 8.11.6-23 from spammers

First please clarify the kind of relay that you want to provide. By relay I
mean local users only, selected internal machines or public mail hub.
Sendmail is the beast that can do practically anything you would like to do.
Regarding relaying to the ISP-s SMTP server masquerade your internal domains
as the domain SMTP server of the ISP is waiting to receive.
Regarding the users, if they are local users of the machine (local accounts
in the mail server) make sure that the access file in /etc/mail directory
contains the localhost. Add to that file also the IP addresses of the client
machines in the internal LAN. Than generate a new access.db file that
sendmail will use. At the same time generate a new sendmail.cf configuration
file starting with sendmail.mc. In this .mc file make sure the feature to
RELAY_HOSTS_ONLY is configured. Disable relaying based on MX and to accept
unresolvable domains. At the end restart the sendmail service.


Sincerely
Mr. Olsi Lulani


-----Original Message-----
From: Keith Mastin [mailto:[email protected]] 
Sent: Tuesday, March 04, 2003 5:41 AM
To: [email protected]
Subject: Re: Securing Sendmail 8.11.6-23 from spammers

Hi Kevin,

> Running RedHat 7.2, with sendmail version 8.11.6-23.72.  Need to secure
> the mail server; so only our group of users
> could send and receive e-mails, and anybody else to get bounced out.
> How do set it up.  Please lead me in the right
> direction. Thanks -- Kevin

To start out with, follow the directions on the recent CERT advisory
regarding sendmail, or switch smtp servers.

You need to specify if you're users are on a private network or if you
want them to be able to relay from remote connections. Relaying from
remote connectins is not advised, and can be a problem with some ISPs. The
practice is getting standardized to having remote users use the local ISP
smtp services and to recieve mail via your server. However, if you insist,
look up SMTP-Auth.

OTOH, I dunno about sendmail, but for postfix the setup for relaying only
for the local network is a matter of editing one line in the conf.

HTH

-- 
Keith Mastin
BeechTree Information Technology Services Inc.
Toronto, Canada
(416)696-6070




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