Use the WebAdmin Interface to configure the POP module. Open the Access page in the Settings realm:
Use the Log Level setting to specify what kind of information the POP module should put in the Server Log. Usually you should use the Major (message transfer reports) or Problems (message transfer and non-fatal errors) levels. But when you experience problems with the POP module, you may want to set the Log Level setting to Low-Level or All Info: in this case protocol-level or link-level details will be recorded in the System Log as well. When the problem is solved, set the Log Level setting to its regular value, otherwise your System Log files will grow in size very quickly. The POP module records in the System Log are marked with the POP tag.
When you specify a non-zero value for the Maximum Number of Channels setting, the POP module creates a so-called "listener". The module starts to accept all POP connections that mail clients establish in order to retrieve mail from your server. The setting is used to limit the number of simultaneous connections the POP module can accept. If there are too many incoming connections open, the module will reject new connections, and the mail client should retry later.
By default, the POP module Listener accepts clear text connections on the TCP port 110. The standard TCP port number for secure POP connections is 995, but it is not enabled by default. Follow the listener link to tune the POP Listener.
The POP module supports the STARTTLS command that allows client mailers to establish a connection in the clear text mode and then turn it into a secure connection.