Somewhat OT email addresses

[Rick Stevens]

On Thu, 2006-02-16 at 12:19 -0500, Jeff Kinz wrote:
> On Thu, Feb 16, 2006 at 01:29:32PM +1100, Graeme Nichols wrote:
> > Hello Folks,
> > 
> > I know this is somewhat OT but I was wondering if it is possible to send 
> > an email with an address in the following format; username@[IP address]
> > 
> > I have been fiddling around because a person with whom I was writing to 
> > has suddenly become unknown, possibly because of DNS failure, I'm not 
> > sure, and the mail is returned undeliverable as the domain is unknown. 
> > They are having the same problem sending mail to me.
> > 
> > I did a ping on my ISP's SMTP mail server and while there was a 100% 
> > failure rate on the packets, most probably due to some firewall setting, 
> > I was given the IP address, in this case, 203.12.160.34
> > 
> > I sent a test email to name at 203.12.160.34 but it bounced with the 
> > following error;
> 
> 
> 
> Graeme, I see one issue here that you would need to fix, assuming you
> are trying to send am email to someone other than yourself.
> 
> You need to enter the IP address of their domain (or their domain's SMTP
> server), not the IP of your ISP's SMTP server.

Graeme, Jeff's right.  You can't send mail to YOUR SMTP server and
expect it to go out.

If sending mail to "yourfriend at theirdomain.tld" doesn't work, you're
probably having an issue with DNS.  A quick test is if you can surf the
web on your machine.  If not, then you definitely have a DNS issue.
This can be caused by several factors: you haven't configured the DNS
on your machine properly (this is the "/etc/resolv.conf" file), or you
have DNS blocked by a firewall somewhere (either via iptables on your
machine or by the firewall on your router or modem...possibly both).

Your /etc/resolv.conf file should contain AT A MINIMUM, one line:

	nameserver ip-address-of-your-ISP's-DNS-server

For example:

	nameserver 64.7.192.162

Ideally, you'd have two or three lines, one for each of your ISP's DNS
servers:

	nameserver 64.7.192.162
	nameserver 64.7.192.163

If you don't know your ISP's DNS server addresses, ask them for them.
If you still can't get them, use the lines above.  They're for our
DNS servers and I don't mind if you use them.  Being the wonderful human
being I am, I won't even charge you for their use!  :-)

Next, you have to check your firewall settings.  On your local machine,
use "iptables -L -n".  You MUST permit TCP and UDP connections to port
53 on your machine for DNS to work.  Appropriate lines to add to your
/etc/sysconfig/iptables file are:

	-A INPUT -p tcp -m tcp --dport 53 -j ACCEPT
	-A INPUT -p tcp -m tcp --sport 53 -j ACCEPT
	-A INPUT -p udp -m udp --dport 53 -j ACCEPT
	-A INPUT -p udp -m udp --sport 53 -j ACCEPT

Also check the firewall on your router or cable/DSL modem and verify
they allow incoming and outgoing TCP and UDP messages using port 53.

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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-     I.R.S.: We've got what it takes to take what you've got!       -
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