Why would you want to use pop3.el instead of an external movemail?
   
   Richard Pieri <ratinox@peorth.gweep.net> says:
   It does not require an external program, which is important on certain
   versions of Emacs running on certain operating systems that cannot
   properly handle inferior processes. It has a running count, x of y, of
   messages downloaded; feedback on a process is always a good thing. It
   does not convert your incoming mailbox to Babyl format. It does not
   pass password information to an external process insecurely.
   
   Why would you not want to use pop3.el instead of an external movemail?
   
   It does not handle multiple maildrops, so if you get your mail from
   multiple POP servers, or from a POP server and a local spool, it may
   not work right. A fix is on the to-do list.
   
   If you use an "expensive" authentication scheme such as KPOP
   (Kerberized POP). KPOP is not going to happen until such time as
   Kerberos is incorporated directly into Emacs.
   
   Using pop3.el
   
   Configure Gnus to use the external movemail program per documentation,
   then add the following line to your ~/.gnus:
   
   (setq nnmail-movemail-program 'nnmail-pop3-movemail)
   
   The following variables may need to be set manually if they are not
   inherited from your environment (or are simply incorrect or
   undefined).
   
   pop3-maildrop
   Your POP3 login name. Inherited from user-login-name, $LOGNAME, $USER;
   otherwise nil. Change this if your POP login is different from your
   local login.
   
   pop3-mailhost
   Server from which you get your mail. Inherited from $MAILHOST;
   otherwise nil.
   
   pop3-port
   Port your POP3 server is on. Defaults to 110.
   
   nnmail-pop-password-required
   't' if you need to supply a password. Defaults to nil. You will
   probably need to make this 't'.
   
   pop3-authentication-scheme
   authentication scheme, either 'pass or 'apop.
   
   pop3.el/nnmail-pop3-movemail currently does not support multiple
   maildrops.