Using Telnet to connect to Exchange 2003 POP3 mailboxes and using SMTP to send e-mail for troubleshooting purposes


Some basic information about POP3 and SMTP


POP3


Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server. Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).


There are two versions of POP. The first, called POP2, became a standard in the mid-80’s and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.


Source: http://www.webopedia.com/TERM/P/POP2.html


Beginning with Exchange 2003 we have to activate POP3 support after the Exchange installation, because Microsoft has disabled some services for security reasons (POP3 communication is unencrypted per Default – but you can use TLS to ensure security).


SMTP


Short for Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.


Source: http://www.webopedia.com/TERM/S/SMTP.html


Let’s begin


Connecting to POP3


Open Telnet (Start – Run – CMD – Telnet) and write the following line:


TELNET Servername.Domain.TLD 110 (in our example TELNET London.nwtraders.msft 110).




Figure 1: Connecting to your Exchange Server via POP3


What do we see here?


+OK                                             – The Exchange Server accepts Connection to Port 110


Exchange Server 2003 POP3           – It is a Exchange 2003 Server


Version 6.5.7226.0                         – The Exchange Version Number


London.nwtraders.msft                   – The FQDN of the Exchange Server


These are some helpful information about our connection.


Let’s go further:




Figure 2: POP3 communication


What do we see here?


USER MSEXchangeORG     – The name of the user to connect to the mailbox


PASS Fake001                  – The password of the user (transmitted unencrypted over the network)


LIST                                 – Lists all E-Mails in the mailbox


RETR 1                             – Display the selected E-Mail


A very interesting part is the displayed body of the E-Mail. You can see the encapsulation of the E-Mail, MIME type, Message ID and much more helpful information.


POP commands































USER


The User you would like to connect to


PASS


The password of the user (transmitted unencrypted over the network)


STAT


Overview over the POP3 mailbox


LIST


Displays every message in listform


RETR


Displays selected message (RETR 1)


DELE


Deletes selected message (DELE 1)


NOOP


NO Operation


RSET


Undo DELE function


QUIT


End POP3 Session


Connecting to SMTP


Open Telnet (Start – Run – CMD – Telnet) and write the following line:


TELNET Servername.Domain.TLD 25 (in our example TELNET London.nwtraders.msft 25).




Figure 3:
EHLO commands


SMTP supports two verbs: HELO an EHLO


The HELO or EHLO verbs in SMTP are how the client identifies itself to the server. Clients that use single-label domain names, or domain names that the server cannot look up in the DNS database, are broken or misconfigured.


EHLO is the successor of the HELO verb and supports many more commands. The supported EHLO verbs are different from Mailserver to Mailserver. Exchange 2003 supports the EHLO verbs displayed in (Figure 3).


A very important EHLO verb is AUTH. AUTH lists the supported authentication methods for connecting to the SMTP Server. Exchange 2003 supports GSSAPI, NTLM and LOGIN.


Some ISP SMTP servers doesn’t support AUTH. They use SMTP after POP. SMTP after POP authenticates a user through a successful POP3 connection and lets him use the SMTP protocol with the applied credentials through the POP3 connect.


In our example we use the basic HELO command to connect.




Figure 4: Write a e-mail through telnet


What do we see here?


220 London.nwtraders.msft            – the Server listens on the given SMTP port


Microsoft ESMTP Mail Service         – This Server supports Extended SMTP


Version: 6.0.3790.0 ready             – This SMTP Service is hosted by Windows 2003


HELO                                           – Initiates connection (requires domain name by most SMTP


servers)


250 London.nwtraders.msft            – Server accepts connections on IP address 192.9.200.116


MAIL FROM: [email protected]       – The Sender of the Message


RCPT TO: [email protected]          – The Reciepient of the Message


DATA:                                          – Input e-mail data for subject and body


SUBJECT:                                     – the subject line of the message


Enter the data for the message body. At the end of the message click <CRLF> “.” <CRLF>


The message will be transmitted through the destination address through exchange.


SMTP commands














































HELO


Identifies the Client


MAIL


Specifies Mail Sender


RCPT


The Reciepient of the message


DATA


The Data part of the message


RSET


Resets message transmiting


VRFY


Verifies e-mail address


EXPN


Expand a mailing list


DSN


Delivery Status Notification


HELP


Displays help


NOOP


NO Operation


TURN


Mail TURN


ETRN


Extended TURN


VERB


Verbose Mode


QUIT


End SMTP Session


Conclusion


Connecting to POP3 Mailboxes and sending E-Mails through SMTP with the help of Telnet will give you a good understanding about the functions of these processes. I like Telnet to troubleshoot POP3 and SMTP issues.


Related Links


POP3 RFC
http://www.faqs.org/rfcs/rfc1939.html


SMTP RFC
http://www.faqs.org/rfcs/rfc821.html


Administering POP3/SMTP/IMAP
http://www.microsoft.com/technet/prodtechnol/exchange/2000/maintain/13x2kada.mspx

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