Troubleshooting

Before contacting technical support, please review the following steps for troubleshooting your SMTP and POP3 accounts.

Overview

Telnet is the best tool for troubleshooting SMTP and POP3 problems because it has no GUI overhead and because it allows the user to see exactly how the mail server is responding.  However, it can also be destructive; the lack of GUI means no error checking, no warnings and no undo.  What is done, is done. So be careful.

Also, you will need to discuss your testing plans with your mail administrator first.  If you do not do so, your mail administrator may suspect an attacker is trying to infiltrate the mail systems and react accordingly.

Using Telnet to test SMTP

In this test, you will send a test email to be deleted later via POP3.  Text you enter is displayed in bold print using a monospace font; always press the Enter key at the end of the line.  Responses from the mail server are displayed in normal print using a monospace font.  All commands are typed in a Command window at the command prompt.

Warning:  The backspace and delete keys do not work in telnet.  You must type everything correctly the first time; so if you make a mistake, press Enter and let the server return a syntax error.

telnet smtp.mailserver.com 25

Trying ???.???.???.???...

Connected to smtp.mailserver.com.

Escape character is ‘^]’.

220 smtp.mailserver.com ESMTP Sendmail ?version-number?; ?date+time+gmtoffset?

You may need to declare where you are sending the email from, but per RFC822-RFC1123 it is not required.  If you skip this step on servers that require it, you may get a response like: Nice people say hello first.

HELO local.domain.name

250 smtp.mailserver.com Hello your.domain.name [ip.address], pleased to meet you

MAIL FROM: YourEmail@domain.com

250 2.1.0 mail@your.domain.com... Sender ok

RCPT TO: TheirEmail@otherdomain.ext

250 2.1.0 mail@otherdomain.ext... Recipient ok

DATA

Subject: Test Message

After entering the previous line, press Enter twice instead of just once.  Remember the subject text because you will need it to identify your test message when deleting it in the POP3 test.

This is a test message from the Mail Administrator.  It is only a test.

To tell the mail server that you have completed the message, enter a single period on a line all by itself and then press Enter, as shown here:

.

250 2.0.0 ???????? Message accepted for delivery

To close the connection and exit Telnet, type the following and press Enter:

Quit

221 2.0.0 smtp.mailserver.com closing connection

Connection closed by foreign host.

Error codes you may encounter during this process include:

501 nouser@nosuchplace.ext...

Domain you are sending from must exist as many servers will do a reverse lookup to verify its validity.

503 Need MAIL before RCPT

Recipient has been specified before the sender; you must always specify the sender first.

550 YourEmail@domain.com...

Relaying denied.  The mail server has refused to relay mail for you.  This can occur for a number of reasons, but the most common reasons are:  not using this provider for an internet connection, not using an email address or IP address provided by the owner of the server, or the ISP does not allow Mail Relay.

Check with the recipient of the message.  Depending on the servers, the message may show up without sender information in the display.  This is purely cosmetic and not an error.  If you wish, you can add these details by including a From: line prior to the Subject: line.

Using Telnet to Test POP3

The Telnet commands for POP3 are different than those for SMTP and can be destructive.  Remember, there is no GUI application layer to prompt for confirmation or allow an undo.  For this test, only the minimum steps required to verify a connection are shown.

This test includes deleting the test message you sent during the SMTP test above.  If you lose the connection to the mail server before issuing the QUIT command, the server should not delete any messages.  However, although a message should not be deleted until the QUIT command is received, some servers may delete the message anyway.

In the following, commands and other text you should enter will be in bold print using a monospace font; responses from the server will be normal print using the same monospace font.  Actual text of the responses may vary slightly depending on the brand and version of the mail server you are using.  For each bold-faced line that you are supposed to type, press the Enter key afterward.

telnet POP3.mailserver.com 110.

A failure will be indicated by the following response.  Refer this issue to your System Administrator:

Could not open connection to the host on port 110.

Otherwise, if the command was successful, the response will look like this:

+OK Microsoft Exchange 2000 POP3 server version 6.0.6249.0 (pop3.mailserver.com) ready.

USER username

This must be the first command you enter after connecting with the server.  Supply your email user name, without the @domain.com portion, in place of the word username in the example above.

PASS password

This must be the next command after USER.  Supply your email password in place of the word password.  The password may be case sensitive. Note: This is clear text so you will see your password as you type it.

STAT

The response to this command follows the format:  +OK #msgs #bytes, where #msgs is the number of messages in the mailbox and #bytes is the total number of bytes used by all of the messages.  Example:

+OK 3 345910

LIST

The response to the LIST command sends one line for each message, specifying the message number and its size (in bytes).  The last line sent is a single period on a line by itself.  For example:

+OK 3 messages

1 1205

2 305

3 344400

.

RETR msg#

Use the RETR command to identify the test message you sent earlier.  The server will respond by displaying the message whose number you specified.  This includes all of the message header information.  If  you sent the test message shown in the SMTP section above, the text should be short enough that it will not scroll off the screen, so you should be able to verify you retrieved the correct message.

DELE msg#

Once you identify the test message, use the DELE command to mark that message for deletion, substituting its number for the msg# field shown above.  This can be an effective way to get rid of a message that is causing problems.

Note that the message is only marked for deletion; it will not actually be deleted until you send the Quit command.  At that point, the message will be permanently deleted from the server and will be irretrievable.

RSET

You can issue the RSET command to revoke any DELE commands you entered.  Any messages marked for deletion in this session will be unmarked so that they will not be deleted when you issue the Quit command.

Quit

Use the Quit command to close the connection and exit Telnet.  Any messages still marked for deletion will be permanently deleted from the server at this time.

+OK Microsoft Exchange 2000 POP3 server version 6.0.6249.0 signing off.