Network Troubleshooting

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Q: You are a network support technician for a college with 4000 users scattered over five locations. A group of users from the downtown location has called your help desk, complaining that they cannot send or receive messages from the Internet, although they can receive messages on the college's internal mail system. List the steps you will take to troubleshoot this problem and describe why each step is necessary. Suppose that your troubleshooting methodology leads you to determine that the problems were caused by a malfunctioning gateway. Suggest ways in which the problem could have been prevented.

Steps to troubleshoot the malfunction:-
Aside from repairing a corrupted Exchange database, mail flow and
email performance issues are the most challenging Exchange Server
problems to diagnose. If users aren't receiving their email, the list
of possible causes is endless. But it is also true that if you got
message from your local sever then it minimizes the problem. Your
receiving end protocol (like POP3) is working.
It's usually pretty easy to tell if your spam filter is too
aggressive or if an Exchange server is configured to filter out
certain types of email messages. On the other hand, if the problem
is related to the SMTP virtual server configuration on an Exchange
server within your organization, the problem is a lot more difficult
to diagnose and treat.

These are the following steps to Troubleshoot Mail Flow:

STEP 1: How to locate an email message in the SMTP queues?
STEP 2: Troubleshooting the DSN Message Pending Submission queue.
STEP 3: Troubleshooting the Failed Message Retry queue.
STEP 4: Troubleshooting the Local Delivery queue.
STEP 5: Troubleshooting the Messages Awaiting Directory Lookup queue.
STEP 6: Troubleshooting the Messages Waiting To Be Routed queue.
STEP 7: Troubleshooting the Final Destination Currently Unreachable queue.
STEP 8: Troubleshooting the Messages Pending Submission queue.
STEP 9: Troubleshooting Remote Destination queues

STEP 1: How to locate an email message in the SMTP queues

Before you can use a message's location to troubleshoot the Exchange
server, you must locate the email message. The message can be located
in any one of a server's many different SMTP queues.

To hunt for a message,
go to Exchange System Manager ->
Administrative Groups->
your administrative group ->
Servers ->
the problematic server ->
Queues.

When you select the Queues container, Exchange System Manager will
display all of the server's SMTP queues in the console's details
pane. The Queues container displays the selected server's entire SMTP
queues.
When you select the Queues container, you'll initially receive some
summary information that will tell you how many email messages are in
each queue, the cumulative size of all of the messages within the
queue, and the date and time that the oldest message was placed into
the queue.
The summary information by itself can be valuable because it can give
you hints as to which SMTP queues might be having problems. For
example, if you see an extremely large queue or a queue that has held
email for a long time, Exchange Server may be having problems
processing the messages in that queue.
This brings me to my next point. If you have a particular branch of
your organization complaining that email is not being received or
that messages that are not being delivered, then the first thing you
need to do is to figure out where the email is going.
Determining where the messages are located is simple if your server
happens to be like mine and only has one message queued. But if you
have dozens of messages flowing through the SMTP queues at any given
time, you will have to do a little detective work to find the missing
email.

The easiest way of locating these email messages is to click the Find
Messages button shown in Figure A. When you do, you will see a dialog
box similar to the one that's shown in Figure B.

STEP 2: Troubleshooting the DSN Message Pending Submission queue

Exchange Server uses the DSN Message Pending Submission queue for
non-delivery reports (NDRs). When Exchange Server needs to send an
NDR to someone, the NDR message is placed into this SMTP queue prior ...