Sendmail的配置文件 sendmail.cf 算得上“臭名昭著”，看看这个文件一定会让你头大，几乎没有人从头来写这个文件。关于 sendmail.cf 的详细内容，参见：Sendmail Installation and Operation Guide --- THE WHOLE SCOOP ON THE CONFIGURATION FILE。

通过使用 m4 宏处理命令，由宏文件 sendmail.mc 来生成复杂的配置文件 sendmail.cf，一切变得简单多了。

/etc/mail/sendmail.mc 文件即是原始宏文件。生成配置文件 sendmail.cf 的命令为：

$ m4 sendmail.mc > sendmail.cf

默认的配置文件仅仅能在本机发送邮件，如果需要更强的功能，需要修改宏文件：sendmail.mc

缺省的sendmail.mc文件：

divert(-1)                                     
dnl This is the sendmail macro config file. If you make changes to this file,
dnl you need the sendmail-cf rpm installed and then have to generate a
dnl new /etc/sendmail.cf by running the following command:
dnl
dnl        m4 /etc/mail/sendmail.mc > /etc/sendmail.cf
dnl
include(`/usr/share/sendmail-cf/m4/cf.m4')
VERSIONID(`linux setup for Red Hat Linux')dnl  
OSTYPE(`linux')                                
dnl Uncomment and edit the following line if your mail needs to be sent out
dnl through an external mail server:
dnl define(`SMART_HOST',`smtp.your.provider')  
define(`confDEF_USER_ID',``8:12'')dnl          
undefine(`UUCP_RELAY')dnl
undefine(`BITNET_RELAY')dnl
define(`confAUTO_REBUILD')dnl
define(`confTO_CONNECT', `1m')dnl
define(`confTRY_NULL_MX_LIST',true)dnl
define(`confDONT_PROBE_INTERFACES',true)dnl
define(`PROCMAIL_MAILER_PATH',`/usr/bin/procmail')dnl
define(`ALIAS_FILE', `/etc/aliases')dnl        
dnl define(`STATUS_FILE', `/etc/mail/statistics')dnl
define(`UUCP_MAILER_MAX', `2000000')dnl
define(`confUSERDB_SPEC', `/etc/mail/userdb.db')dnl
define(`confPRIVACY_FLAGS', `authwarnings,novrfy,noexpn,restrictqrun')dnl
define(`confAUTH_OPTIONS', `A')dnl
dnl TRUST_AUTH_MECH(`DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
dnl define(`confAUTH_MECHANISMS', `DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
dnl define(`confTO_QUEUEWARN', `4h')dnl
dnl define(`confTO_QUEUERETURN', `5d')dnl
dnl define(`confQUEUE_LA', `12')dnl
dnl define(`confREFUSE_LA', `18')dnl
dnl FEATURE(delay_checks)dnl
FEATURE(`no_default_msa',`dnl')dnl
FEATURE(`smrsh',`/usr/sbin/smrsh')dnl        
FEATURE(`mailertable',`hash -o /etc/mail/mailertable.db')dnl
FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable.db')dnl 
FEATURE(redirect)dnl
FEATURE(always_add_domain)dnl                
FEATURE(use_cw_file)dnl                      
FEATURE(use_ct_file)dnl                      
dnl The '-t' option will retry delivery if e.g. the user runs over his quota.
FEATURE(local_procmail,`',`procmail -t -Y -a $h -d $u')dnl
FEATURE(`access_db',`hash -o /etc/mail/access.db')dnl
FEATURE(`blacklist_recipients')dnl
EXPOSED_USER(`root')dnl
dnl This changes sendmail to only listen on the loopback device 127.0.0.1
dnl and not on any other network devices. Comment this out if you want
dnl to accept email over the network.
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')
dnl NOTE: binding both IPv4 and IPv6 daemon to the same port requires
dnl       a kernel patch
dnl DAEMON_OPTIONS(`port=smtp,Addr=::1, Name=MTA-v6, Family=inet6')
dnl We strongly recommend to comment this one out if you want to protect
dnl yourself from spam. However, the laptop and users on computers that do
dnl not have 24x7 DNS do need this.
FEATURE(`accept_unresolvable_domains')dnl     
dnl FEATURE(`relay_based_on_MX')dnl
MAILER(smtp)dnl
MAILER(procmail)dnl
Cwlocalhost.localdomain

修改该配置如下：

dnl Dmworldhello.net
dnl Dwmail
dnl define(`confDOMAIN_NAME', `$w.$m')dnl                    
... ...
FEATURE(`domaintable',`hash -o /etc/mail/domaintable')       
... ...
FEATURE(`genericstable',`hash -o /etc/mail/genericstable')   
... ...
GENERICS_DOMAIN_FILE(`/etc/mail/genericsdomain')             
... ...
dnl  DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')     
... ...
FEATURE(`accept_unqualified_senders')dnl                     
... ...
define(confMAX_HOP,30)                                       
... ...
Cwlocalhost.localdomain your_real_domain                      
... ...