TODO
====

o Implement the volume for the console beep
o Test if the 'execcommand' variable in the configuration file points to
  a valid executable (double-click action).
o In configure.in, is the check to "sys/types" necessary?
o In pop3.c, gethostbyname() blocks for a long time if network is unavailable.
  Try alternative to this blocking mode (timeout value?).
o The volume setting in the configuration file is in percentage, but it is not computed
  as a logarithmic function in file sound.c (dB).
o Use the same Tx and Rx buffers for POP3 and IMAP4 (check the sizes...)