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Re: [vox-tech] MTA + ... (was: more security questions (DNS & securitythread)
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Re: [vox-tech] MTA + ... (was: more security questions (DNS & securitythread)

Hey Cylar,

Glad you got Apache back up.

On Mon, 22 Aug 2005, Cylar Z wrote:
> As to sendmail, am I to understand that to run it
> "locally," I'd turn the daemon back on, but close the
> SMTP port on the iptables firewall?

I'm not sure how mail transports work locally.  I *think* you can turn off
that port altogether because of the way mail transports work, but you may
have to open it up locally ( a.k.a localhost).  Try the former
and see if you can e-mail from a user account to another user account; if
you can't, then open up

> Assuming your
> answer to that is "yes," do I also safely assume that
> it's the same way with other services that are to be
> run "locally?" I think that's what you said but I want
> to be absolutely sure, before I risk opening any holes
> in my security perimeter that could be exploited.

Well, there's two ways, right?:

   1. Make the daemon listen on only.

   2. Make the daemon listen on (any IP), but block it off
      from non- IPs using the firewall.

#1 is more elegant over #2, I think.  But why not combine the best of
both methods:

   3. Make the daemon listen on only, AND block it off
      from non- IPs using the firewall.

So do #3 if you can.  To get daemons to listen on only, you'll
need to configure each daemon to listen on only; but some
daemons may not have that option.  And blocking off non- IPs is
done through the firewall.

Sendmail is a special case because I don't think it needs to open up ANY
port to transport mails on the same computer; I think it's necessary only
when transporting mails over the network to open up port 25.  But again,
I'm not sure about that so try it out.  (Or maybe someone here knows the

> Second, I'm interested in adding a mail server that
> actually can communicate with the outside world. I've
> been hearing that sendmail config is hard and that I
> should use PostFix instead. Your opinion please.

I'm probably not the best person to ask since I haven't done much e-mail
configuring.  From what I've heard at various places it's a good idea to
move away from sendmail.  Postfix is a good alternative.  I personally use
Exim but only because that's the Debian default.  You probably can't go
wrong with either Postfix or Exim, though I've had this impression over
the years that Postfix is a little more configurable and powerful while
Exim is a bit simpler to configure.  But that could be an old idea or even
a complete jibbrish so I wouldn't put much weight on it without others'


Mark K. Kim
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