Sendmail/Exim and IP-Address
hunter kreie
plug-discuss@lists.plug.phoenix.az.us
Tue, 29 Jan 2002 22:10:34 -0700
Damn, that's exactly what I was going to say, to the bit, beautiful.
-----Original Message-----
From: plug-discuss-admin@lists.plug.phoenix.az.us
[mailto:plug-discuss-admin@lists.plug.phoenix.az.us] On Behalf Of Shawn
Rutledge
Sent: Tuesday, January 29, 2002 7:47 PM
To: plug-discuss@lists.plug.phoenix.az.us
Subject: Re: Sendmail/Exim and IP-Address
On Tue, Jan 29, 2002 at 04:20:51PM -0700, Roderick Ford wrote:
> I started looking into setting up an MX on my LAN, by reading info at
> Sendmail.org. I have a fairly static IP address, i.e. not guaranteed
to
> NEVER change, but never does. It is VERY (34 char) long,
> "cpe-24-221-41-162.az.sprintbbd.net", and
>
> (1) I'm wondering if mail sent here would have to be
@this_long_address, or
> if there is a way to alias it shorter.
Yes. You need a registered domain. For example I own ecloud.org,
and my DNS records look like this:
ecloud.org NS ns1.hn.org
ecloud.org NS aux1.hn.org
www.ecloud.org CNAME ecloud.org
ecloud.org MX ecloud.org 10
ecloud.org A 68.3.203.249
That's one way to do it... just map your domain to your "static" IP,
and forget about cpe-blah-blah entirely. Or, you could maybe make
your domain a CNAME for cpe-blah-blah, and also have an MX record
which says that cpe-blah-blah can accept mail for your-domain.
I'm using HammerNode (hn.org) for DNS service. Seems to be OK so
far. Used to use GraniteCanyon but they had some problems.
Now if only the SMTP port wasn't being blocked... (by Cox AFAIK)
> (2) Will I be able to configure a mail server so that
> (2a) fetchmail will forward retrieved mail to the mail server
I haven't done that yet but why bother with fetchmail? If you pull off
having your own domain, just have mail sent to you@your-domain.
As I use fetchmail right now, I just run a separate copy for each
user.
But I saw in the fetchmail docs that it's possible to run it as a
system daemon and have it grab mail from multiple POP accounts and
deliver to specific users. For example
user foo there is bar here
or something like that, in the config file.
> (2b) where it can be retrieved by the user on the LAN?
Sure, of course. Mail for each user ends up in one big file
/var/spool/mail/username. Simple mailers like elm or mutt simply
read messages from this file, and modify this file to mark messages
read, delete them, etc. Lockfiles are used to make sure that
sendmail/exim
and mutt/elm don't write to the same file at the same time. If your
users want to use mailers on other machines, rather than logging in
to your mail server and running mutt or some such, then you need a
POP or IMAP server. Different ones work differently; but the simplest
POP server simply leaves the mail in the same spool file, and delivers
messages from it upon request. Other mail systems (Cyrus, maybe some
others) have other ways of organizing the mail on disk.
> (3) Can the mail server be on the DNS server as long as they have the
same
> name and don't slow each other down?
Sure, neither is very resource-intensive.
> (4) IF mail does have to go to webmaster@this_long_address, then it is
over
> 40 characters...
Why is there a 40-character limit? I don't ever remember encountering
anything like that, but don't know for sure.
> (4a) too long?
> (4b) Then mail will hit the router and be forwarded according to
the
> port/firewall setting to the mailserver box, right?
I don't think routers can do mail delivery; I think sendmail is
what pays attention to the DNS MX records. For example, suppose
somebody@xyz.edu is trying to send you mail. The sendmail process
running at xyz.edu sees that the highest-priority (lowest-numbered)
MX record for your-domain points to mail.your-domain. So it will
try to open an SMTP connection to mail.your-domain. If it fails
to establish a connection, then it will have another look at the
DNS records and see if there is a secondary MX (higher numbered).
If it finds one, it will try to open an SMTP connection to that;
and so on, until it either succeeds or runs out of servers to try.
If it still can't deliver it then it simply has to leave the mail
in a file on disk (taking up disk space at xyz.edu) until it gets
around to trying again. By default, sendmail will keep trying for
5 days and then ultimately give up and delete the message.
SMTP sessions are conversations occurring on TCP connections; and
the TCP connection is the level with which the routers are
concerned, but AFAIK they usually don't much care what sort of
data is being sent over those TCP connections that they are
maintaining.
--
_______ Shawn T. Rutledge / KB7PWD
ecloud@bigfoot.com
(_ | |_) http://ecloud.org
kb7pwd@kb7pwd.ampr.org
__) | |
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