毫無(wú)疑問，近一段時(shí)期以來(lái)，日益盛行。據(jù)估計(jì)，垃圾郵件占全部郵件的80%到90%，很多郵件在對(duì)付由最新的垃圾郵件所引起的額外負(fù)擔(dān)問題上存在著很大的困難，而且垃圾郵件過(guò)濾器如SpamAssassin并不能如以前那樣識(shí)別大部分的垃圾郵件。幸運(yùn)的是，我們可以在郵件傳輸代理(Mail Transfer Agent，MTA)層次上阻止大量的垃圾郵件，例如通過(guò)使用黑名單、在發(fā)送者和接收者的域上運(yùn)行測(cè)試等。這樣做的一個(gè)額外的優(yōu)勢(shì)是它可以降低郵件服務(wù)器的負(fù)荷，因?yàn)槔]件過(guò)濾器需要查看的郵件更少。
基礎(chǔ)工作
本文將討論怎樣配置Postfix(2.x和1.x)，在垃圾郵件進(jìn)入服務(wù)器之前阻止它。不過(guò)，在將本文所討論的方法運(yùn)用到您的郵件服務(wù)器中之后，您應(yīng)該檢查您的郵件日志，確保合法的用戶郵件不會(huì)被阻止。
您可以查看如下鏈接得到一些指導(dǎo)性的信息：
http://www.howtoforge.com/virtual_postfix_antispam
如下的鏈接包含另外一些反垃圾郵件解決：
http://www.howtoforge.com/taxonomy_menu/1/78/24
Postfix 2.x
打開/etc/postfix/main.cf文件，在其中增加如下的幾行(如果相關(guān)的配置存在，就替換之):
vi /etc/postfix/main.cf
[...]
smtpd_helo_required = yes
disable_vrfy_command = yes
strict_rfc821_envelopes = yes
invalid_hostname_reject_code = 554
multi_recipient_bounce_reject_code = 554
non_fqdn_reject_code = 554
relay_domains_reject_code = 554
unknown_address_reject_code = 554
unknown_client_reject_code = 554
unknown_hostname_reject_code = 554
unknown_local_recipient_reject_code = 554
unknown_relay_recipient_reject_code = 554
unknown_sender_reject_code = 554
unknown_virtual_alias_reject_code = 554
unknown_virtual_mailbox_reject_code = 554
unverified_recipient_reject_code = 554
unverified_sender_reject_code = 554
smtpd_recipient_restrictions =
reject_invalid_hostname,
reject_unknown_recipient_domain,
reject_unauth_pipelining,
permit_mynetworks,
permit_sasl_authenticated,
reject_unauth_destination,
reject_rbl_client multi.uribl.com,
reject_rbl_client dsn.rfc-ignorant.org,
reject_rbl_client dul.dnsbl.sorbs.net,
reject_rbl_client list.dsbl.org,
reject_rbl_client sbl-xbl.spamhaus.org,
reject_rbl_client bl.spamcop.net,
reject_rbl_client dnsbl.sorbs.net,
reject_rbl_client cbl.abuseat.org,
reject_rbl_client ix.dnsbl.manitu.net,
reject_rbl_client combined.rbl.msrbl.net,
reject_rbl_client rabl.nuclearelephant.com,
permit
[...]
然后重新啟動(dòng)Postfix:
/etc/init.d/postfix restart
Postfix 1.x
打開/etc/postfix/main.cf，并在其中加入如下幾行(如果相關(guān)的配置已經(jīng)存在就替換之)：
vi /etc/postfix/main.cf
[...]
smtpd_helo_required = yes
disable_vrfy_command = yes
strict_rfc821_envelopes = yes
invalid_hostname_reject_code = 554
multi_recipient_bounce_reject_code = 554
non_fqdn_reject_code = 554
relay_domains_reject_code = 554
unknown_address_reject_code = 554
unknown_client_reject_code = 554
unknown_hostname_reject_code = 554
unknown_local_recipient_reject_code = 554
unknown_relay_recipient_reject_code = 554
unknown_sender_reject_code = 554
unknown_virtual_alias_reject_code = 554
unknown_virtual_mailbox_reject_code = 554
unverified_recipient_reject_code = 554
unverified_sender_reject_code = 554
maps_rbl_domains =
multi.uribl.com,
dsn.rfc-ignorant.org,
dul.dnsbl.sorbs.net,
list.dsbl.org,
sbl-xbl.spamhaus.org,
bl.spamcop.net,
dnsbl.sorbs.net,
cbl.abuseat.org,
ix.dnsbl.manitu.net,
combined.rbl.msrbl.net,
rabl.nuclearelephant.com
smtpd_recipient_restrictions =
permit_sasl_authenticated,
permit_mynetworks,
reject_invalid_hostname,
reject_non_fqdn_hostname,
reject_non_fqdn_sender,
reject_unknown_sender_domain,
reject_unknown_recipient_domain,
reject_maps_rbl,
check_relay_domains
[...]
然后重新啟動(dòng)Postfix:
/etc/init.d/postfix restart