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550 Host unknown

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 ----- <techadmin@CompanyDomain.biz>
    (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 mail.CompanyDoamin.biz 25"
Would someone please give me a hand with this?

Here are the results of all the tests:

nslookup results
nslookup mail.CompanyDomain.biz

Non-authoritative answer:
Name:    mail.companydomain.biz
Address:  w.x.y.z

More nslookup results
> set type=mx
> companydoamin.biz
Server:  inside-DNS.company.local
Address:  10.x.x.x

Non-authoritative answer:
CompanyDomain.biz       MX preference = 0, mail exchanger = mail.CompanyDomain.biz

CompanyDomain.biz       nameserver = ns31.domaincontrol.com
CompanyDomain.biz       nameserver = ns32.domaincontrol.com
mail.CompanyDomain.biz  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      @      mail.CompanyDomain.biz


--output from SMTP Diag via mxtoolbox.com--

220 mail.CompanyDomain.biz 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:
HELO please-read-policy.mxtoolbox.com
250 mail.CompanyDomain.biz Hello recover.mxtoolbox.com [] (may be forged), pleased to meet you [31 ms]
MAIL FROM: <supertool@mxtoolbox.com>
250 2.1.0 <supertool@mxtoolbox.com>... Sender ok [16 ms]
RCPT TO: <test@example.com>
550 5.7.1 <test@example.com>... Relaying denied. IP name possibly forged [] [31 ms]
221 2.0.0 mail.CompanyDomain.biz closing connection [16 ms]

--Port Scan via mxtoolbox.com

       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 verify-email.org--

Result: Ok
MX record about CompanyDomain.biz exists.
Connection succeeded to mail.CompanyDomain.biz SMTP.
220 mail.CompanyDomain.biz ESMTP Sendmail 8.14.3/8.14.3; Sun, 14 Feb 2010 21:14:11 -0600
> HELO verify-email.org
250 mail.CompanyDomain.biz Hello web409.opentransfer.com [], pleased to meet you
> MAIL FROM: <check@verify-email.org>
=250 2.1.0 <check@verify-email.org>... Sender ok
> RCPT TO: <techadmin@CompanyDomain.biz>
=250 2.1.5 <techadmin@CompanyDomain.biz>... Recipient ok

--Results from DNS Watch.info--

Searching for mail.CompanyDomain.biz. A record at G.ROOT-SERVERS.NET. [] ...took 31 ms
Searching for mail.CompanyDomain.biz. A record at B.GTLD.biz. [] ...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 g.gtld-servers.net. [] ...took 165 ms
Searching for mail.CompanyDomain.biz. 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', `smtp.covad.net')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

Email ServersSoftwareEmail Protocols

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Last Comment

8/22/2022 - Mon

Have you verified that you can send mail to that user from another user that's on the same Exchange server?  A 550 error could also be associated with the user as with the host.

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This morning a got a pleasant surprise. The in box of the test account (techadmin@CompanyDoamin.biz) not only had mail, from all the test that I sent, it also had mail from 2 days past. The only explanation I have is that the DNS information was not totaly propagated "world wide".  I did not change any configurations sice I posted last night. Anyway the problem that I have left is listed below, after sending mail to an external address:

#550 4.4.7 QUEUE.Expired; message expired in unreachable destination queue. Reason: A matching connector cannot be found to route the external recipient ##"

As it plainly states, the "Connector" settings in Exchange, is not quite right, I will visit those and post the outcome as soon as it becomes available.

It turns out as I said in the previous post it started work when the DNS propagated. I setup the connector settings in exchange .. The problem is solved.

Your help has saved me hundreds of hours of internet surfing.