常用的电子邮件协议有SMTP、POP3、IMAP4，它们都隶属于TCP/IP协议簇，默认状态下，分别通过TCP端口25、110和143建立连接
新浪：
pop3 pop.shia.com
smtp smtp.sina.com
qq:
pop3 pop.qq.com
smtp smtp.qq.com
telnet smtp.qq.com 25
helo hello
auth login
Y2hlbmppbmh1aTEwNQ==
mail from:<1036735352@qq.com>
rcpt to:<1361339802@qq.com>
data
subject:hello,you!
my name is zhang lian quan
.
协议 地址 ssl !ssl
imap imap.163.com 993 143
smtp smtp.163.com 465/994 25
pop3 pop.163.com 995 110
mkdir -p /root/.certs/
echo -n | openssl s_client -connect smtp.163.com:465 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > ~/.certs/163.crt
certutil -A -n "GeoTrust SSL CA" -t "C,," -d ~/.certs -i ~/.certs/163.crt
certutil -A -n "GeoTrust Global CA" -t "C,," -d ~/.certs -i ~/.certs/163.crt
certutil -L -d /root/.certs