* * * * *
                                        
                           Overly pendantic commands
                                        
I was called by R (guy I work for) to double check the email system since it
looked like (to him) that it wasn't working at all and no emails were being
sent (order confirmations, etc). I start checking, and from what I could
tell, the email system was working fine. I placed a few test orders from a
few sites and got the confirmation email. And from the mail logs, it looked
like it was sent off to R as well.

But he wasn't getting them.

A few more tests while talking to R seemed to confirm that email sent to him
from the server was being accepted by his ISP (Internet Service Provider),
but R was still not getting them. Which indicates to me that his ISP is
filtering out spam and for whatever reason, email from this server was being
flagged as spam and not delivered.

I then did the following on the server to check something out:

> [root]rnm.miami:~>hostx -t mx XXXXXXXXXXXX
> XXXXXXXXXXXX            MX      20 mail2.XXXXXXXXXXXX
>  !!! XXXXXXXXXXXX MX host mail2.XXXXXXXXXXXX is not canonical
> XXXXXXXXXXXX            MX      10 mail.XXXXXXXXXXXX
>  !!! XXXXXXXXXXXX MX host mail.XXXXXXXXXXXX is not canonical
> 

Hmmm … odd. Double check the zone file.

> $TTL 3600
> @	IN	SOA	ns1.XXXXXXXXXXXX. root.XXXXXXXXXXXX. (
> 			2004091801 ; Serial
> 			10800	; Refresh
> 			3600	; Retry
> 			3600000 ; Expire
> 			3600 )	; Minimum
> 
> 	IN	NS	ns1
> 	IN	NS	ns2
> 	IN	NS	ns3
> 	IN	MX	10 mail
> 	IN	MX	20 mail2
> 
> mail	IN	A	XXX.XXX.XXX.XXX
> mail2	IN	A	XXX.XXX.XXX.XXX
> ns1	IN	A	XXX.XXX.XXX.XXX
> ns2	IN	A	XXX.XXX.XXX.XXX
> ns3	IN	A	XXX.XXX.XXX.XXX
> 

Nothing out of the ordinary. The RR (Resource Record)s for mail and mail2
aren't CNAMEs (which is a common mistake). They look fine to me, and running
host on outside machines report back fine:

> [root]linus:~>host -t mx XXXXXXXXXXXX
> XXXXXXXXXXXX            MX      20 mail2.XXXXXXXXXXXX
> XXXXXXXXXXXX            MX      10 mail.XXXXXXXXXXXX
> 

A quick Google [1] didn't reveal anything I already didn't know (most of the
problems I found were CNAME errors). So, I started playing around with the
zone file. Make a change, same error. Make another change, same error. It was
only when I removed all references to mail and mail2 when I discovered the
problem.

By then, I was doing hostx -G -S -C -A -L 1 zone (which verifies the entire
zone) and getting back errors about mail and mail2. Which shouldn't be
happening, as I had just removed all references to them in the zone file.
There was only one other place where they were defined—/etc/hosts. Once I
removed those entries from /etc/hosts, the problem went away:

> [root]rnm.miami:~>hostx -t mx XXXXXXXXXXXX
> XXXXXXXXXXXX            MX      20 mail2.XXXXXXXXXXXX
> XXXXXXXXXXXX            MX      10 mail.XXXXXXXXXXXX
> 

Talk about your overly pendantic host command.

[1] http://www.google.com/search?hl=en&ie=UTF-8&q=%22MX+host%22+%22is+not+canonical%22+&btnG=Google+Search

Email Sean Conner at sean@conman.org

.