To test a POP3 connection using telnet open a command window or shell terminal and type the following

telnet pop.domain.com 110

Where pop.domain.com is the FQDN (Fully Qualified Domain Name) or IP address of the server you wish to test.

110 also assumes default pop3 configuration.

You will be greeted with somthing similar to:

Connected to localhost.
Escape character is '^]'.
+OK dovecot ready.

Now you need to authenticate

USER buzz
+OK
PASS thisismypassnorealyitis...honest
+OK Logged in.

Once logged in you can now make use of the following commands

STAT This command will respond as follows (colour added)

STAT
+OK <span style="color: #3333ff;">12</span> <span style="color: #009900;">3571942</span>

This indicates there are 12 emails in the mail box with a total size of 3571942 bytes.

LIST This command will list a line for each message with its number and size in bytes

+OK 12 messages:
1 1209
2 307
3 32715
4 218
5 15937
6 3469
7 98724
8 54356
9 1128
10 560
11 1150309
12 2213010
.

RETR 11 This is the retrive command, in this case this will display the contents of email 11

DELE 11 This is the delete command, in this case this will mark email 11 for deletion (will not delete it).

RSET This is the reset command, this will clear any delete flags you have set.

QUIT This command will logout of the current account, any emails marked for deletion will now be deleted.