Re: SMTP server or "forwarding"?

From: Jonathan Berry (berryja_at_gmail.com)
Date: 08/28/05

  • Next message: Benjamin Rappe: "FC_4 DVD" 
    Date: Sat, 27 Aug 2005 17:57:51 -0500
To: For users of Fedora Core releases <fedora-list@redhat.com>

    On 8/27/05, Les Mikesell <lesmikesell@gmail.com> wrote:
    > On Sat, 2005-08-27 at 12:31, Jonathan Berry wrote:
    >
    > > > If your ISP can't keep their mail server running, find another ISP.
    > >
    > > Actually, I mean not available as in not there, rather than not
    > > functional at times. And switching ISPs is not an option for someone
    > > on a University network (see other emails).
    >
    > So you want a roaming client, like a laptop that might be
    > connected elsewhere or a client you configure on a different
    > network to be able to send to 'your' ISP's server? In the

    Basically, yes.

    > 'fixed client at another location' case you may be able to
    > send though a local smtp server. The roaming on is a

    That would be ideal, but I do not know if such a server is available.

    > little harder. Of course the easy fix is to get a gmail.com
    > account and use that from everywhere. If you need your

    Yes, that is something I had thought about. That is definitely a
    possible solution.

    > own connection, you need to first decide if you want to
    > handle SMTP sending as a special case or if you really
    > want full access to your base machine from the internet.
    > In the latter case, you would probably want to set up
    > openvpn on the laptop and your base machine. Make that

    I might want to do that sometime, but I don't need that much right now.

    > connection and everything else works as it would locally,
    > and it is encrypted across the internet. You can also

    It can also be a little slow, but yeah.

    > use ssh and port-forward smtp (and a few other things)
    > though it with the setup controlled by the client request.
    > >From your client:
    > ssh -L25:isp_ipaddress:25 your_server
    > and be sure that is connected before you send from your
    > mail program which you configure to send to localhost:25.

    This is interesting. How exactly does it work? Is this for
    connecting to the ISP SMTP or to my own server that I setup?

    > > Right. But the client I want to connect to it is not on the local
    > > LAN. It needs to come across the internet.
    > >
    > > >
    > > > It is easy to do this either with iptables or xinetd's 'redirect'
    > > > function, but I don't see the point here. If you have one email
    > > > client, point it to the ISP. If you want a local server, use
    > > > its smart_host feature to send everything outbound through the ISP.
    >
    > > Obviously, I was not very clear on what I wanted to do. Sorry about
    > > that. Your two choices do not describe what I want. So can iptables
    > > or the xinetd redirect take traffic and send it back out the same
    > > interface to my ISP's SMTP server? That sounds like what I might want
    > > if so.
    >
    > With iptables it is better to work on different interfaces for
    > port forwarding. Xinetd doesn't really care and you could arrange
    > for an odd high port to magically connect to your ISP's smtp port
    > with a 'redirect' entry but it would not be secure at all and

    I like this solution, nice and simple. I have it setup right now
    (confined to my local network by my hardware firewall for now). I
    certainly do not want to help spammers and/or viruses in spreading,
    but how much of a real security risk is this? Do spammers/viruses
    look for SMTP servers on strange ports? I know I see a lot of knocks
    on my firewall logs to all kinds of ports, but I have no idea what
    they are trying to do. Is there a way to set this up with a lot of
    logging to where I could see what traffic was going through? How does
    this look to the SMTP (is the connection seen from my IP or the
    originating IP)? I want to get in trouble for helping spammers even
    less than I want to help spammers :). I could always lock down the
    from IP range, and tweak it if I need it from a different location via
    ssh. Any thoughts on this?

    > I wouldn't recommend it. A better alternative would be to
    > use 'stunnel' to accept ssl connections with a client certificate

    This sounds interesting too. I like the idea of having some auth that
    would be simple to setup. I guess I'll do some reading up on stunnel
    and see if I can get that working. Anyone have any experience with
    stunnel?

    > required and forward t o your isp, or run your own mail server
    > with ssl on port 465 or port 587 with TLS and require authenticated
    > logins for SMTP forwarding. Most current mail clients support

    Might as well use Gmail if I'm to go that far. Less to have to keep track of.

    > this (I even do it with my palm-based treo phone's wireless
    > internet). I don't remember enough about the setup to give you
    > a step-by-step, but you should be able to find HOWTO's for
    > stunnel and the sendmail setup for those approaches.
    >
    > Also, for something even easier - your ISP may have a web
    > interface for roaming access.

    Yeah, they do and it is a pathetic interface and very slow. But the
    idea was to use a regular MUA rather than webmail.

    Thanks for the ideas,
    Jonathan 

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