rmail-pop-password-required

rmail-pop-password-required is a variable defined in `rmail.el'.
Its value is

nil

• This variable is an alias for `rmail-remote-password-required'.
• This variable is obsolete since 22.1;
  use `rmail-remote-password-required' instead.

Documentation:
Non-nil if a password is required when reading mail from a remote server.

You can customize this variable.