Technical data

Configuring and Managing the POP Server
18.1 Key Concepts
18.1.1 POP Server Process
The POP server is installed with SYSPRV and BYPASS privileges and runs in the
TCPIP$POP account, which receives the correct quotas from the TCPIP$CONFIG
procedure. The POP server is invoked by the auxiliary server.
The POP server uses security features provided in the protocol and in the
OpenVMS operating system, as well as additional security measures. These
methods provide a secure process that minimizes the possibility of inappropriate
access to a user’s mail file on the served system.
You can modify the POP server default characteristics and implement new
characteristics by defining the system logical names outlined in Section 18.3.
18.1.2 How to Access Mail Messages from the POP Server
To access mail messages from the POP server, you configure a user name and
password, or the POP shared secret-password string, into your client mail
application.
Your client system opens the TCP connection and attempts to access the server
by entering applicable POP commands such as USER (user name) and PASS
(password), or APOP (shared secret password). In addition, POP supports the
UID command, which some POP clients use, where the UID (user identification)
that POP creates for each mail message is a concatenation of the user name and
the date of arrival.
Once your client system opens the TCP connection, the POP server issues the
following greeting:
+OK POP server ready TCPIP V5.1 [hostname and IP_Address]
By default, the POP server reads mail from the user’s OpenVMS NEWMAIL
folder. If you do not instruct the POP server to delete the mail, the server
either moves the mail to the MAIL folder (if the logical name TCPIP$POP_USE_
MAIL_FOLDER is defined) or keeps it in the NEWMAIL folder (if the logical
name TCPIP$POP_LEAVE_IN_NEWMAIL is defined). These logical names are
described in Section 18.3.
18.1.3 How the POP Server Initiates and Manages a TCP Connection
The POP server starts the service by listening on TCP port 110. The client
initiates a connection when it wants to make use of the POP service. The POP
server sends either a greeting message confirming the connection (a message with
the +OK prefix) or a message that the connection was not successful (a message
with the -ERR prefix).
POP permits only two user name and password authorization attempts per TCP
connection. After the second failure, POP closes the connection. Once connected,
the client and server exchange commands and responses.
When the POP server detects a blocked TCP connection, it suspends output to
the connection for 2 seconds to allow it to unblock. Upon retry, if the connection
is still blocked, the POP server waits 4 seconds before trying again, and so on up
to 32 seconds. If the connection is still blocked after 32 seconds, the POP server
shuts down the connection and sends an error message to the log file, allowing
other client connections to continue to operate.
18–2 Configuring and Managing the POP Server