E-Mail Troubleshooting Example
In a short period of time, a large
number of network users call to report that they cannot send email, but they
can receive it. Remember, that the network has separate servers for sending and
receiving email. There is an SMTP server that is used to send e-mail and a POP3
server is used to receive and save e-mail.
Since the users are receiving
email, it is doubtful that the POP3 server is malfunctioning. The problem of
sending email could be isolated to the server running the SMTP protocol.
Testing the physical, data link, and network layers reveals no problems.
To test the Transport layer, attempt to Telnet into the SMTP server
through port 25. A hello message is not received from the server. This
indicates problems at either the transport or application layer.
Verify
the following:
- Is the router denying access to port 25?
- Is the e-mail client properly configured?
- Is the address being used to Telnet the SMTP server correct?