Re: CNAME records (was: Re: dynamic DNS within a non-dynamic domain)
On Wed, 4 Mar 1998, George Bonser wrote:
> On Thu, 5 Mar 1998, Remco Blaakmeer wrote:
[question about CNAME records and MTAs rewriting the From: header when the
hostname is a CNAME]
> One thing to do is to make sure that you have the following in your
> own /etc/hosts file:
>
> 130.89.222.95 blaakmeer.student.utwente.nl cal011205.student.utwente.nl
Yes, it actually is:
130.89.222.95 blaakmeer.student.utwente.nl blaakmeer cal011205.student.utwente.nl cal011205 remco
> If you are using sendmail, it will grab the FIRST name listed when it
> canonifies the address. Also, you might use mail -v to send someone
> an email outside of your network, this allows you to see exactly what
> what your machines gives the other mailhost in the MAIL FROM: part of
> the transaction.
I am using smail. See the results of my tests below.
> If you are using NIS and it is using an NIS lookup ahead of DNS, it will
> also grab the first name listed after the IP address in the table.
No, there is no NIS anywhere near my computer.
> If you are using a smarthost that uses SunOS with Sun's sendmail. you are
> likely out of luck. I will go into the reasons for that in private email
> if this is the case but the only way around it is to get your hostname
> listed first in the domain's NIS hosts.byname map if it uses NIS for
> host resolution.
No, also no Sun machines in sight. The smarthost is, AFAIK, a HP machine
that runs HP/UX and has this greeting:
220 driene.student.utwente.nl 5.67b/IDA-1.5 Sendmail is ready at Sat, 7 Mar 1998 05:30:38 +0100
BTW, my computer has this greeting:
220-blaakmeer.student.utwente.nl Smail-3.2.0.100 (#2 1998-Jan-13) ready at Sat, 7 Mar 1998 05:40:00 +0100 (CET)
220 ESMTP supported
Ok, now for the tests. The conclusion of the tests is this:
If I locally send mail to myself, the From: header is not rewritten.
If I send mail to another host, the From: header is rewritten after smail
got the message.
When fetchmail fetches my mail, the From: header is rewritten before smail
gets the mail.
When I fetch the mail using telnet to the pop-3 port, the From: header is
already rewritten.
The mail 'at another host' is sent to j.r.blaakmeer@student.utwente.nl,
which is also my e-mail address. I have fetchmail running as daemon to get
mail from that address to my computer.
Note that the From: header is rewritten to the address that the CNAME
points to, not the FQDN for my computer. You'd say they are the same, but
they are not. The FQDN is all lowercase letters, while the name that the
CNAME points to starts with a capital. Because DNS lookups are not case
sensitive this doesn't matter normally, but now I can see the difference
between them.
130.89.222.95 is cal011205.student.utwente.nl
CNAME: blaakmeer.student.utwente.nl -> Cal011205.student.utwente.nl
I have compiled a full description of what I did to test this and what the
result was, but I don't want to send it to the list as it is rather
lengthy. Should I send it to somebody? Or can I send a 10kB mail to the
list?
Remco
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