SMTP: Troubleshooting the TCP/IP Layer of the Mail Gateway

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Summary

If the SMTP gateway cannot connect to the mail routing host or receive incoming mail, the TCP/IP layer may not be working properly. This article describes how to troubleshoot the IP and TCP layers.

More Information

Testing the IP Layer

To test the IP layer, use the PING command from the gateway computer up to the host and from the host down to the gateway computer:

  1. Test the network adapter with the loopback IP address:
    ping 127.0.0.1
    If this test fails, then the problem is related to the network interface card (NIC).
  2. Test the connection on the local subnet:
    ping <ip address>
    where <ip address> is the IP address of a host on the same subnetwork. If this fails, then the subnet mask is configured incorrectly.
  3. Test the connection to the default gateway:
    ping <gateway ip address>
    where <gateway ip address> is the IP address of the default gateway, also known as a router. If this test fails, then you have an incorrect IP address for the default gateway, or the gateway is down.
  4. Test the connection to a remote subnet:
    ping <remote ip address>
    where <remote ip address> is the IP address of a host on another subnet. If this fails, then the connectivity problem is most likely on the remote side.
  5. Test the DNS name resolution:
    ping <host.domain>
    where <host.domain> is something like smarthost.microsoft.com If this fails, then either the DNS entry in the TCP/IP configuration is incorrect or the DNS server is having problems providing name service at this time.
If this works, you receive a response indicating how many packets were bounced off the destination host. Successful completion of these commands means the IP layer is working correctly.

Testing the TCP Layer

To test the TCP layer, use the TELNET command with a "25" after the host ID or IP address to specify the mail socket. Run it from the gateway computer up to the host and from the host down to the gateway computer:
telnet tcpiphost.company.com 25 telnet msmailgwy.company.com 25
NOTE: You can't run the second command unless the gateway is running.



If this succeeds, you receive the response "220 ...." from the destination host. Type quit to end the test. Successful completion means the TCP layer is working.


NOTE: If you use -cd (debug) and -lacsy (full logging) the 220 response is recorded in the LOG file.
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ID članka: 115492 – Zadnji pregled: 17. jun. 2014 – Revizija: 1

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