[time-nuts] Jack Hudler

[John Ackermann N8UR]

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