阻擋垃圾郵件

以前會使用 ORDB 來阻擋一些垃圾郵件，換新機器後，這些設定都還原了（而且 ORDB 也已經宣佈解散囉）。果然，垃圾郵件如雪片般飛來，每天都有 300 封左右，砍不勝砍。今天又砍了快 600 封，非常浪費時間，決定把阻擋垃圾郵件的機制重建起來。

第一個作法，就和過去使用 ORDB 作法一樣，讓 sendmail 在收信時參考網路上的 Open Relay 黑名單，拒收使用 Open Relay 的來信，這已經可以擋掉大半了。作法是編輯 /etc/mail/sendmail.mc，在「MAILER(smtp)dnl」之前加入以下資訊：

FEATURE(`dnsbl',`dnsbl.sorbs.net',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://dnsbl.sorbs.net/')dnl
FEATURE(`dnsbl',`sbl.spamhaus.org',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://sbl.spamhaus.org/')dnl
FEATURE(`dnsbl',`xbl.spamhaus.org',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://xbl.spamhaus.org/')dnl
FEATURE(`dnsbl',`DNSBL.SORBS.NET',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://DNSBL.SORBS.NET/')dnl
FEATURE(`dnsbl',`blackholes.mail-abuse.org',`550 5.7.1 Mail from $& {client_addr} rejected based on external blacklist - See also http://blackholes.mail-abuse.org/')dnl
FEATURE(`dnsbl',`dialups.mail-abuse.org',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://dialups.mail-abues.org/')dnl
FEATURE(`dnsbl',`relays.mail-abuse.org',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://relays.mail-abuse.org/')dnl
FEATURE(`dnsbl',`dul.maps.vix.com',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://dul.maps.vix.com/')dnl
FEATURE(`dnsbl',`dynablock.njabl.org',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://dynablock.njabl.org/')dnl
FEATURE(`dnsbl',`dsbl.dnsbl.net.au',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://dnsbl.dnsbl.net.au/')dnl
FEATURE(`dnsbl',`ipwhois.rfc- ignorant.org',`550 5.7.1 Mail from $& {client_addr} rejected based on external blacklist - See also http://www.ordb.org/')dnl
FEATURE(`dnsbl',`bl.spamcop.net',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://bl.spamcop.net/')dnl
FEATURE(`dnsbl',`list.dsbl.org',`550 5.7.1 Mail from $&{client_addr} rejected based on external blacklist - See also http://list.dsbl.org/')dnl

然後敲「make」，產生新的 sendmail.cf，再重啟 sendmail 「service sendmail restart」即可。

這樣還不足夠，因為仍有許多 MTA 雖不是 Open Relay，但是專門寄出垃圾郵件。於是參考了這份文件，嚐試著把 SpamAssassin 和 milter-greylist 架設起來，看能不能如文章中所說得：「怕你會無聊，因為已經沒有可殺的 spam 了」。

最後再參考這個網站，增加 SpamAssassin 的 rule，就大功告成囉，接下來就是驗收成果啦。