Install SMTP server with relay 安裝 SMTP 伺服器並啟用轉發功能

A SMTP server can send mail from local machine by default.
It also can relay mail from other machine/device if relay function is enabled.

SMTP 伺服器預設只可以允許本機送出郵件。
如果開啟轉發功能的話，就可以讓外部機器經由本機送出郵件。


OS: CentOS 5.3
作業系統: CentOS 5.3


Reference
http://apt.nc.hcc.edu.tw/web/student_server_centos/student_server_centos.html#smtp



Step 1. Install sendmail,m4 and sasl programs.
安裝 sendmail 與修改設定檔的 m4 程式，還有認證的 sasl 程式。

yum -y install sendmail sendmail-cf m4 cyrus-sasl

Step 2. add local host name in local-host-names file.

在local-host-names file加入本機名稱

vi /etc/mail/local-host-names

your.machine.hostname

Step3. modify sendmail template configuration (not direct used by sendmail)

修改 sendmail 的設定檔 (並非 sendmail 直接使用的設定檔)

vi /etc/mail/sendmail.mc

dnl TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl 

=>

TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')

dnl define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')

=>

define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')

dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')

=>  DAEMON_OPTIONS(`Port=smtp,Addr=0.0.0.0, Name=MTA')

Step 4. transfer .mc to cf for sendmail

利用 m4 把設定檔轉成 sendmail 使用的的設定檔

m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

Step 5. edit relay access configuration (not direct used by sendmail)

編輯哪台機器可以轉發 的權限 (並非 sendmail 直接使用的設定檔)

vi /etc/mail/access

Connect:localhost.localdomain RELAY
Connect:localhost RELAY
Connect:127.0.0.1 RELAY

Connect:remote.machine.ip RELAY

Step 6. transfer access database for sendmail

利用 makemap 把設定檔轉成 sendmail 使用的設定檔

makemap hash /etc/mail/access < /etc/mail/access

Step 7. start sendmail and sasl service

重新執行 sendmail 和 sasl 服務

/etc/rc.d/init.d/saslauthd restart
/etc/rc.d/init.d/sendmail restart

p.s. you can enable sendmail and sasal on boot

設定開機執行 sendmail 與sasl

chkconfig saslauthd on
chkconfig sendmail on

Step 8. add firewall rule for allow specific IP to send mail from this machine.

加入防火牆規則以允許特定 IP 可以透過此台寄送郵件

vi /etc/sysconfig/iptables

-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 25 -j ACCEPT

Step 9. restart firewall

重新啟動防火牆

service iptables restart

p.s. test SMTP server from other machine

從別的機器測試是否可連接到本機 port 25

telnet your.smtp.ip 25

Trying your.smtp.ip...
Connected to 140.109.53.5 (140.109.53.5).
Escape character is '^]'.
220 localhost.localdomain ESMTP Sendmail 8.13.8/8.13.8; Thu, 3 Jan 2013 14:55:16 +0800
=> Works

telnet your.smtp.ip 25Trying your.smtp.ip...
telnet: connect to address your.smtp.ip: No route to host
=> Something worong

*. check mail queue

查看是否有未寄出的信

sendmail -bp

*. checking mail

查看 log

cat /var/log/maillog