troubleshooting Question

550 Host unknown

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cyberchrisrockFlag for United States of America asked on
Email ServersSoftwareEmail Protocols
4 Comments1 Solution3195 ViewsLast Modified:
I have built a Linux Fedora 12 box as a MTA for the company to facilitate a new Exchange
server that is on the inside network. The MTA is siting on the DMZ and can ping the Exchange
server and visa versa. When I try to send mail to the test account which is setup on the exchange
server, I get the follwoing error:

----- The following addresses had permanent fatal errors ----- <>
    (reason: 550 Host unknown)

I have used every tool and test that I can think of or find, and I cannot fathom why this error
exist or continue to.The company has a Bonded T1 service from Covad. I called and spoke to them
about this but they had no real answer except to buy more services and had over the in house mail
operation. I included their smtp information in the "Smart Host" section of the Sendamil config file.
I have tried to be as comprehensive as possible so that I can get an answer as quick as possible,
without fraustrating you guys and myself. I was also able to telnet to the MTA via
"telnet 25"
Would someone please give me a hand with this?

Here are the results of all the tests:

nslookup results

Non-authoritative answer:
Address:  w.x.y.z

More nslookup results
> set type=mx
Address:  10.x.x.x

Non-authoritative answer:       MX preference = 0, mail exchanger =       nameserver =       nameserver =  internet address = w.x.y.z
--DNS Records SPF Text value--

v=spf1 a mx ptr mx:w.x.y.z ip4:w.x.y.z-all

--DNS A Record--

mail      w.x.y.z

--DNS MX Record--

0      @


--output from SMTP Diag via

220 ESMTP Sendmail 8.14.3/8.14.3; Sat, 13 Feb 2010 22:34:54 -0600

 Not an open relay.
 0 seconds - Good on Connection time
 0.094 seconds - Good on Transaction time
 OK - resolves to
 Warning - Reverse DNS does not match SMTP Banner

Session Transcript:
250 Hello [] (may be forged), pleased to meet you [31 ms]
250 2.1.0 <>... Sender ok [16 ms]
550 5.7.1 <>... Relaying denied. IP name possibly forged [] [31 ms]
221 2.0.0 closing connection [16 ms]

--Port Scan via

       25      smtp      Success      31 ms

These ports were closed:

       21      ftp      Timeout      0 ms
       22      ssh      Timeout      0 ms
       23      telnet      Timeout      0 ms
       53      dns      Timeout      0 ms
       80      http      Timeout      0 ms
       110      pop3      Timeout      0 ms
       143      imap      Timeout      0 ms
       139      netbios      Timeout      0 ms
       389      ldap      Timeout      0 ms
       443      https      Timeout      0 ms
       587      msa-outlook      Timeout      0 ms
       1433      sql server      Timeout      0 ms
       3306      my sql      Timeout      0 ms
       3389      remote desktop      Timeout      0 ms
       8080      webcache      Timeout      0 ms

--Result from

Result: Ok
MX record about exists.
Connection succeeded to SMTP.
220 ESMTP Sendmail 8.14.3/8.14.3; Sun, 14 Feb 2010 21:14:11 -0600
250 Hello [], pleased to meet you
=250 2.1.0 <>... Sender ok
> RCPT TO: <>
=250 2.1.5 <>... Recipient ok

--Results from DNS

Searching for A record at G.ROOT-SERVERS.NET. [] ...took 31 ms
Searching for A record at [] ...took 120 ms
Searching for NS32.DOMAINCONTROL.COM. A record at H.ROOT-SERVERS.NET. [] ...took 95 ms
Searching for NS32.DOMAINCONTROL.COM. A record at [] ...took 165 ms
Searching for A record at NS32.DOMAINCONTROL.COM. [] ...took 92 ms


---Partial SendMail config---

      dnl # Uncomment and edit the following line if your outgoing mail needs to      
Other      dnl # be sent out through an external mail server:      
Other      dnl #      
Other      dnl define(`SMART_HOST', `')dnl      
Other      dnl #      
Define      define(`confDEF_USER_ID', ``8:12'')dnl      
Other      dnl define(`confAUTO_REBUILD')dnl      
Define      define(`confTO_CONNECT', `1m')dnl      
Define      define(`confTRY_NULL_MX_LIST', `True')dnl      
Define      define(`confDONT_PROBE_INTERFACES', `True')dnl      
Define      define(`PROCMAIL_MAILER_PATH', `/usr/bin/procmail')dnl      
Define      define(`ALIAS_FILE', `/etc/aliases')dnl      
Define      define(`STATUS_FILE', `/var/log/mail/statistics')dnl      
Define      define(`UUCP_MAILER_MAX', `2000000')dnl      
Define      define(`confUSERDB_SPEC', `/etc/mail/userdb.db')dnl      
Define      define(`confPRIVACY_FLAGS', `authwarnings,novrfy,noexpn,restrictqrun')dnl      
Define      define(`confAUTH_OPTIONS', `A')dnl

NOTE THE "SMART_HOST" section in the sendmail config above.

Thanks in Advance


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