sendmail local mta mode only

[Dan Strick]

On Thu, 25 Mar 2004 19:24:08 -0700, David Bear wrote:
>>
> I would like to run the stock sendmail freebsd has as a local MTA
> only... ie I don't want to listening on ANY real/public interface for
> mail.  I do want it to handle delivery of local messages to local
> accounts -- and handle sending messages destined for external systems.
>
> any pointers ?
>>

Recent versions of the sendmail are installed non-setuid-root for
security reasons (paranoia probably justified in the case of sendmail).
Since local mail delivery requires root privilege in the general case,
all local mail is forwarded to the smtp port on the local host for
local delivery.  If there is no sendmail daemon running as root and
listening on the local smtp port, local mail cannot be delivered.
Even on a non-networked single user workstation this is inconvenient
because cron job output is delivered via email.

I think you can modify /etc/mail/freebsd.submit.mc to deliver local
mail the old way and make /usr/libexec/sendmail/sendmail setuid root.
This may be documented /usr/src/contrib/sendmail/src/SECURITY.
It looks ugly to me and may create worse security problems than
running a sendmail daemon that listens on the smtp port.

The standard FreeBSD version of sendmail is built with libwrap support.
If your primary concern is hackers on other systems abusing your sendmail
daemon, you can modify /etc/hosts.allow to permit smtp port access only
from the local host.  Life is too short to spend most of it trying to
understand obscure sendmail documentation.

Dan Strick
strick at covad.net