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| 7.4 |  | Troubleshooting TCP/IP Application Layer Problems |
| 7.4.3 |  | Troubleshooting e-mail problems |

Troubleshooting e-mail problems can be easy. However, sometimes there are other factors that can affect users from properly retrieving or sending e-mail. A mistyped setting can cause a lot of problems. Careful configuration is key to the success of using an e-mail server.

E-Mail Troubleshooting Example
In a fairly 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 the port number for the SMTP protocol (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?