域为tzsky.com，本机IP为14.1.1.251
 
vi sendmail.mc
修改一下几项：
TURST_AUTH_MECH('EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
define('confAUTH_MECHANISMS', 'EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
DAEMON_OPTIONS('Port=smtp,Addr=14.1.1.251, Name=MTA')dnl
DAEMON_OPTIONS('Port=submission, Name=MSA, M=Ea')dnl
LOCAL_DOMAIN('tzsky.com')dnl、
 
m4 sendmail.mc > sendmail.cf
 
vi sendmail.cf
修改最大信息大小
0 MaxMessageSize=20000000
 
生成认证：
make -C /etc/pki/tls/certs/ dovecot.pem
 
vi /etc/dovecot.conf
修改以下几项：
ssl_cert_file = /etc/pki/dovecot/certs/dovecot.pem
ssl_key_file = /etc/pki/dovecot/private/dovecot.pem
 
重启三个服务：
service sendmail restart
service dovecot restart
service saslauthd restart
 
查看端口状态：
netstat -tupln|grep sendmail
netstat -tupln|grep dovecot
netstat -tupln|grep named
 
客户端上测试：
telnet 14.1.1.251 25
telnet 14.1.1.251 110