если в работе белкопочты у вас возникла такая ошибка :
Warning: getmypid() has been disabled for security reasons in /usr/share/squirrelmail/functions/strings.php on line 469
Warning: Cannot modify header information — headers already sent by (output started at /usr/share/squirrelmail/functions/strings.php:469) in /usr/share/squirrelmail/functions/global.php on line 506
Warning: Cannot modify header information — headers already sent by (output started at /usr/share/squirrelmail/functions/strings.php:469) in /usr/share/squirrelmail/src/redirect.php on line 183
то значит, что у вас отключена данная функция :
online-kiska:/etc/php5/apache2# cat php.ini | grep getmy
disable_functions = exec, system, passthru, scandir, popen, shell_exec, proc_open, proc_close, proc_nice, get_current_user, getmyuid, posix_getpwuid, apache_get_modules, virtual, posix_getgrgid, getmyinode, fileowner, filegroup, getmypid, apache_get_version, apache_getenv, apache_note, apache_setenv, disk_free_space, diskfreespace, dl, ini_restore, openlog, syslog, highlight_file, show_source, symlink, disk_total_space, ini_get_all, get_current_user, posix_uname
удаляем функцию из списка запрещенных и перезагружаем вебсервер.