mail to another machine on the LAN

[Tim]

Tim:
>> I think you want to check that each computer in the equation can resolve
>> its own name, and the other computer's.  Avoid using "localhost" as part
>> of the mail addresses.

Hiisi:
> How to check it?

The dig tool can be used to check DNS queries.  But, you can probably
just try pinging the hostnames, and look at what happens.

e.g. Presuming a host was called "mail", issuing "ping mail" as a
command would produce several lines of output.  The first one would have
the fully qualified domain name and IP address (that it finds out
about), the next few lines the ping results.

[tim at suspishus ~]$ ping mail
PING mail.example.com (192.168.1.2) 56(84) bytes of data.
64 bytes from mail.example.com (192.168.1.2): icmp_seq=1 ttl=64 time=1.43 ms
64 bytes from mail.example.com (192.168.1.2): icmp_seq=2 ttl=64 time=1.19 ms
^C
--- mail.example.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1414ms
rtt min/avg/max/mdev = 1.192/1.313/1.435/0.126 ms

If names and IP addresses are correct, then you'd expect that name
resolution is working fine.  The ping results (timewise) just show
networking responses, not responses from any mail software.


> If it's possible I would like not to create my own DNS server. Looking
> for simple way to solve my problem.

Well, to be honest, I find running a normal DNS server much much simpler
than messing around with hosts files.  It gives me central management of
name resolution, which is particularly useful if I ever need to change
anything.  And for *proper* mail handling, it's essential.  The hosts
file is inadequate - it cannot handle MX enquires, for instance.

I'm not sure if you need the full normal functionality to get local mail
working, it's been years since I've tried to do mail with a crippled
network setup.

In the normal run of things, when you try to mail someone, the mail
server will do a MX record lookup to find out what should handle the
mail.  i.e. If you try to mail johndoe at example.com, mail doesn't simply
get passed off to example.com, a MX lookup is done on example.com to
find the address for example.com's mail server.

There are fallbacks for dealing with a lack of MX records, but how
that's all handled will depend on your mail software.  Old-timer's
standard advice is "when you stop doing things the normal way, all bets
are off."

>> The [bracketing] the IP address after the @ sign ought to work, to use
>> an IP address without name lookups, but I don't know if everything does
>> that trick.

> In my case it seemingly doesn't work.

What tests are you trying?  Obviously what you want to work isn't
working, but what else are you trying to get mail to go through?  The
"mail" command line, a graphical mailer?

First I'd try doing mail on each computer to itself, to see if that
works.  e.g. mail root at localhost

Then, I'd try a similar test (still mailing itself), this time
substituting the computer's own hostname.

  e.g. mail root at computer1 
       and, separately, mail root at computer2 
 
> I saw it when I was trying to send message to <user>@[192.168.3.30]. If
> I send mail to <user>@192.168.3.30 there's no such error in mailog but
> message is returned by MAILER-DAEMON to root.

Does sound rather like you're getting error messages back from different
servers (in one case, your SMTP server talking to another).  You could
try disconnecting your LAN from the ISP to limit what's involved in the
test.

-- 
[tim at localhost ~]$ uname -r
2.6.27.25-78.2.56.fc9.i686

Don't send private replies to my address, the mailbox is ignored.  I
read messages from the public lists.