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Exchange Doesnt receive EXTERNAL Email 'SMTP Host Not Sopecified'

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  • Exchange Doesnt receive EXTERNAL Email 'SMTP Host Not Sopecified'

    Hi all,

    After working with problem for a couple of days now with limited success I thought I'd pose the question here as I have always received a positive response.

    My infrastructure:

    Two domain controllers (running server 2008 x64, both GC, DNS, DHCP servers) DC1 holds all five FSMO roles.
    One Mail server running Server 2008 x64 and Exchange 2007
    A gateway running server 2003 and RRAS

    Exchange itself is configured with the hub transport, client access and mailbox roles. We currently have a BT line with 5 leased static IP addresses. The mail is configured to come in on one of these (assigned by the BT router to our gateway)

    We have a second external mailbox (a catchall) where mail will end up should our exchange server go down

    Everything was working fine on Thursday last week.
    Our Internet (BT) went down on Friday last week. This was due to a problem at the exchange. Whilst BT was fixing it I swapped over to our backup line. I edited the DNS entries for our domain (hosted externally) to route mail through the new internet line (Eclipse). However this didnt work for whatever reason! I changed the DNS entries back to represent BT and waited for them to fix the problem (manually forwading on the mail to our users as it dropped into the catchall external mailbox)

    Finally on Wednesday evening BT fixed the problem and I plugged the BT router back into our gateway. At first everythign seemed fine. Most mail was being received (randomly a few domains were going straight to the catchall box)

    However, mail is no longer being received atall (as of yesterday). I ran some tests:

    On the exchange server in the toolbox the mail acceptance test:
    All results came back ok until the mail acceptance area. Then two error messages labelled 0 and 1 both returned errors 'Mail submission failed: The SMTP host was not specified'

    I can telnet into the companies external ip address on port 25 (and it returns the name of the mail server). However, I cant telnet in on the host name.

    I can also access OWA using the external IP but again not the hostname

    When using the test tools at it also returned results that it didnt think port 25 was open.

    One thing I did do yesterday was to Go to EMC>Server Config>Hub Transport and changed the external DNS lookup from 'Use network card DNS settings' to the IPS's of the external BT DNS servers (specified in the BT router). This was done becase some sent mail (to specific domains) was being bounced back to the comapany with a
    #550 4.4.7 QUEUE.Expired; message expired ## error

    I read on EE where doing this switch had fixed the issue (in an environment similar to mine)

    Dare I say it but does anyone have any ideas?

    Thanks in advance, if you need any more information just shout.

  • #2
    Re: Exchange Doesnt receive EXTERNAL Email 'SMTP Host Not Sopecified'

    Looks like your DNS entries are messed up, since you edited them twice within short time.
    Resolved DNS queries are stored in caches especially at the Internet in several caches, it could take some times to register made changes.

    You could ask your provider for the DNS entries if he is able to speed up the process on his site but you can't do anything on the rest of the net you simply have to wait.


    • #3
      Re: Exchange Doesnt receive EXTERNAL Email 'SMTP Host Not Sopecified'


      Thanks for the fast reply. Thats what I thought as well but I didnt understand why it was getting progressively worse. Its been over 24 hours since I made the last DNS entry change.

      I thought it might be to do with the External DNS lookup settings I changed in EMC>Server Config>Hub Transport

      I did change them back though. Hmmm

      Also I notice this morning that some emails (ironically those from the companies that werent coming through yesterday are not getting through amd the domains that were getting through yesterday (including gmail are going straight into our catcfh all box)

      I'll contact our provider and ask him to confirm how long it should take for the correct DNS entries to replicate properly



      • #4
        Re: Exchange Doesnt receive EXTERNAL Email 'SMTP Host Not Sopecified'

        Ok so I got our provider to force an update on the DNS and now the results from all come back green. I receive a confiormation email too.

        I can now also receive emails from

        However, when I rerun the toolbox test on the exchange box I still get the same error:

        SMTP Host was not specified

        Could this be caused by anything else (ive checked the obvious send connector /receive connector and everything seems to be as it should be)

        I can now telnet into the host name and ip externally.

        I have also never run this exchange test before so I dont know if this SMTP ERROR message was being flagged before the mail problems. I know I cant access the external OWA site from inside the network. I have to use the FQDN/netbios server name.

        Could this be why the exchange test is returning this error?

        Everything else seems to work ...I'll keep an eye but I can receive email now and access the owa site. Just confused about the exchange toolbox error.

        Note there are no error messages in the servers event log and havent been since this issue arose

        Edit: Oops forgot to thank FischFra for the idea so thanks