How to troubleshoot Basic SMTP Delivery Problems

Introduction:
The following are basic steps that a mail admin can take to determine the cause of an SMTP mail delivery problem. This procedure assumes that an Exchange IMS is deployed using DNS lookups, rather than forwarding SMTP to an a third part gateway or relay host. 

Basic things to check:

Is your IMS running?

Is your firewall configured to allow your IMS server to have a dedicated IP address seen from the Internet.

Is your IMS server correctly configured for DNS lookup via it's TCP/IP{ protocol settings?

If your IMS is part of a Microsoft cluster, you need to register all three IP addresses.  That is the IP of each individual node, as well as the cluster server IP.

Are your DNS records in order in order.  Your IMS server should have both, a forward lookup address (A record) as well as a reverse lookup (PTR).

If you are running a file level antivirus application, ensure that your \imcdata folders are excluded, from real time, and scheduled scanning.  Be sure to cover sub-folders as well.

Check SMTP Connnectivity:

  1. Log onto the console of your IMS box and bring up a command window.
     

  2. From the command prompt, run 'nslookup'.  Nslookup will greet you with it's own command prompt.
     

  3. From the nslookup prompt, type 'set type=mx'
     

  4. From the nslookup prompt, type the name of domain you are haveing trouble sending mail to.

> abbaticchio.com
Server: unicom01.schp.com
Address: 10.32.16.167

abbaticchio.com MX preference = 10, mail exchanger = mx01-dom.earthlink.net
abbaticchio.com MX preference = 10, mail exchanger = mx00-dom.earthlink.net
abbaticchio.com nameserver = DNS3.earthlink.net
abbaticchio.com nameserver = DNS2.earthlink.net
abbaticchio.com nameserver = DNS1.earthlink.net
mx01-dom.earthlink.net internet address = 207.217.120.136
mx00-dom.earthlink.net internet address = 207.217.120.135
DNS3.earthlink.net internet address = 207.217.120.13
DNS2.earthlink.net internet address = 207.217.77.12
DNS1.earthlink.net internet address = 207.217.126.11

  1. Start with the server that has the highest mx preference, which would be the lowest number.  (In this case there are two servers with equal preference of MX preference = 10  ).  Find the corresponding 'A Record' from the query, and write down the IP address. (In this case, mx01-dom.earthlink.net internet address = 207.217.120.136 ).
     

  2. Exit out of nslookup, by typing 'exit'.  Proceed to the following link located on this site, and return here when finished.

Conclusion:

The most common point of failure occurs at the DNS level lookup.  Any step in the previous procedure which failed, will needed to be diagnosed and corrected, before any other actions are taken, as these steps check the most basic functions of SMTP communications.  If no problems are found, using the previous steps, try turning up SMTP protocol diagnostic logging for short periods of time, (keep available free disk in mind).  This will generate detailed logs, which contain all SMTP commands processed by your IMS, and what the receiving SMTP servers responses were.