[time-nuts] Jack Hudler
Jack Hudler
jack at hudler.org
Tue Jan 2 22:50:13 UTC 2007
I was astonished at the reduction in junk when they switch over to doing this.
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf
Of John Ackermann N8UR
Sent: Tuesday, January 02, 2007 4:10 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Jack Hudler
Randy Warner said the following on 01/02/2007 03:55 PM:
> The following recipient(s) could not be reached:
>
> Jack Hudler on 1/2/2007 12:45 PM
> There was a SMTP communication problem with the recipient's
> email server. Please contact your system administrator.
> <synergy-gps.com #5.5.0 smtp;553 host is missing reverse dns
> record (see http://www.internetmailserver.net/reverse-dns.html)>
Randy, some mail servers do a check to make sure that the IP address
matching the name, is the same as the name matching the IP address --
it's called a reverse lookup. This is designed to reduce spam and
spoofing; it's arguable whether it does much good.
The problem is that often ISPs don't assign a reverse name unless you
ask them. For example, one of my addresses (that I don't use for an
external server) maps to:
"
jra at flob:~$ nslookup
> mvfma.febo.com
Name: mvfma.febo.com
Address: 24.123.66.141
> 24.123.66.141
141.66.123.24.in-addr.arpa name =
rrcs-24-123-66-141.central.biz.rr.com.
"
That would set off the warning you got from Jack's system because
mvfma.febo.com doesn't have anything to do with
rrcs-24-123-66-141.central.biz.rr.com.
On the other hand, my mail server looks like this:
"
jra at flob:~$ nslookup
> meow.febo.com
meow.febo.com canonical name = febo.com.
Name: febo.com
Address: 24.123.66.139
> 24.123.66.139
Non-authoritative answer:
139.66.123.24.in-addr.arpa name = meow.febo.com.
"
Here, the two match so all is well.
Usually, your ISP is willing to set up a "reverse DNS" record for your
server that will provide a match, but you have to ask them to do that.
Getting that record established should solve the problem reaching Jack,
and possibly others who get mail through a server that does this check.
Hope this helps,
John
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