By default Exchange 2007 POP3 Service use secure Login type(TCP Port 995)

Use Get-POPSettings to verify your POP3 login type.

if you have problem running pop3 using port 110,

it is Suggest you change the pop3 authentication to Plaintext and try again in client,and make sure it’s ok then change to other login type.

here’s some command & example to trouble POP3 connection :

From the Windows task bar, select: Start, Run…, and enter the following:
telnet pop-server-name port#
(Note: if you start Telnet from the browser, the syntax is telnet://pop-server-name:port#

Check your mail settings for the pop-server-name and port#.

Most POP3 servers use port 110.

* You must include the correct port number, usually 110. The default Telnet port number won’t work.
* The syntax varies by how you start the Telnet program. On the Start, Run, you separate the server name and the port number with a Space. In the browser, you separate the server name and the port number with a Colon.

You will want to enable Local Echo so you can see what you type. In the Win95 Telnet program this is under Terminal, Preferences. Also, you may want to turn on logging to capture messages to a text file. In the Win95 Telnet program this is under Terminal, Start Logging

For the connection, and each command that you enter, the mail server will respond:
-ERR 999 message text
for commands it doesn’t like (the 999 is an optional error code that varies), or
+OK message text
if it likes the command. After each response, you can enter a new command.

Note: When entering the following commands to the POP3 server, you may not be able to use the backspace key to fix typing errors. Many POP3 servers do not recognize that. They aren’t expecting a person, but rather another program that doesn’t make typing mistakes. For example, if you key “STS(bs)AT” (where (bs) represents the backspace key), you may see “STAT”, but the POP3 server lilely will report that “STAT” is an unknown command. That’s because the server saw “STS(bs)AT”. If you make a typing error, just hit Enter, let the server report the error, and start the command again. However, if you make a mistake on the USER or PASS command, you won’t likely get a second chance. In that case, enter the QUIT command and start the Telnet program over.

Commands that you can/must use are:

USER userid
This must be the first command after the connect. Supply your e-mail userid (not the full e-mail address). Example: USER john.smith

PASS password
This must be the next command after USER. Supply your e-mail password. The password may be case sensitive.

The following commands may be used as needed:

STAT
The response to this is: +OK #msgs #bytes Where #msgs is the number of messages in the mail box and #bytes is the total bytes used by all messages. Sample response: +OK 3 345910

LIST
The response to this lists a line for each message with its number and size in bytes, ending with a period on a line by itself. Sample response:
+OK 3 messages
1 1205
2 305
3 344400
.

RETR msg#
This sends message number msg# to you (displays on the Telnet screen). You probably don’t want to do this in Telnet (unless you have turned on Telnet logging). Example: RETR 2

TOP msg# #lines
This is an optional POP3 command. Not all POP3 servers support it. It lists the header for msg# and the first #lines of the message text. For example, TOP 1 0 would list just the headers for message 1, where as TOP 1 5 would list the headers and first 5 lines of the message text.

DELE msg#
This marks message number msg# for deletion from the server. This is the way to get rid a problem causing message. It is not actually deleted until the QUIT command is issued. If you lose the connection to the mail server before issuing the QUIT command, the server should not delete any messages. Example: DELE 3

RSET
This resets (unmarks) any messages previously marked for deletion in this session so that the QUIT command will not delete them.

QUIT
This deletes any messages marked for deletion, and then logs you off of the mail server. This is the last command to use. This does not disconnect you from the ISP, just the mailbox.

There are other POP3 commands. For some more information on this topic, see:

RFC 1939 which defines POP3 commands and error codes