sendmail の構築
http://server-setting.info/centos/sendmail_1_simple_setting.html
http://www.server-memo.net/server/server-setting/sendmail/sendmail-setting
http://www.puni.net/~mimori/sendmail/qgroup.html
http://www.asi.co.jp/techinfo/unix/sendmail.html
http://futuremix.org/2003/05/sendmail
http://www.ipa.go.jp/security/fy12/contents/crack/soho/soho/chap3/smtp/sendmail.html
define(`confMIN_QUEUE_AGE', `3m')dnl
define(`confTO_HOSTSTATUS', `10m')dnl
define(`confHOST_STATUS_DIRECTORY', `.hoststat')