关于在java中使用qq企业邮箱发邮件，踩了几个坑，发出来供大家参考。
问题一：能telnet 通 smtp.exmail.qq.com 465，但是发邮件就报错，提示连接smtp失败
Exception in thread "main" javax.mail.MessagingException: Could not connect to SMTP host: smtp.exmail.qq.com, port: 465, response: -1
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2106)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:712)
at javax.mail.Service.connect(Service.java:388)
at javax.mail.Service.connect(Service.java:246)
at javax.mail.Service.connect(Service.java:195)
at javax.mail.Transport.send0(Transport.java:254)
at javax.mail.Transport.send(Transport.java:124)
at com.jiuhou.common.util.mail.SimpleMailSender.sendTextMail(SimpleMailSender.java:55)
at com.jiuhou.common.util.mail.SimpleMailSender.main(SimpleMailSender.java:189)
问题分析和解决方案：
由于出于安全性考虑，qq企业邮箱服务器要求必须要使用 SSL 安全连接（qq邮箱不需要），所以发件时要配置如下参数才可以：
pro.put("mail.smtp.ssl.enable", "true");
说明一个发邮件问题排查技巧，要把mail的debug打开，才能看到整个调试信息：
pro.put("mail.debug", "true");
如下：
DEBUG: JavaMail version 1.5.6
DEBUG: successfully loaded resource: /META-INF/javamail.default.providers
DEBUG: Tables of loaded providers
DEBUG: Providers Listed By Class Name: {com.sun.mail.smtp.SMTPSSLTransport=javax.mail.Provider[TRANSPORT,smtps,com.sun.mail.smtp.SMTPSSLTransport,Oracle], com.sun.mail.smtp.SMTPTransport=javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle], com.sun.mail.imap.IMAPSSLStore=javax.mail.Provider[STORE,imaps,com.sun.mail.imap.IMAPSSLStore,Oracle], com.sun.mail.pop3.POP3SSLStore=javax.mail.Provider[STORE,pop3s,com.sun.mail.pop3.POP3SSLStore,Oracle], com.sun.mail.imap.IMAPStore=javax.mail.Provider[STORE,imap,com.sun.mail.imap.IMAPStore,Oracle], com.sun.mail.pop3.POP3Store=javax.mail.Provider[STORE,pop3,com.sun.mail.pop3.POP3Store,Oracle]}
DEBUG: Providers Listed By Protocol: {imaps=javax.mail.Provider[STORE,imaps,com.sun.mail.imap.IMAPSSLStore,Oracle], imap=javax.mail.Provider[STORE,imap,com.sun.mail.imap.IMAPStore,Oracle], smtps=javax.mail.Provider[TRANSPORT,smtps,com.sun.mail.smtp.SMTPSSLTransport,Oracle], pop3=javax.mail.Provider[STORE,pop3,com.sun.mail.pop3.POP3Store,Oracle], pop3s=javax.mail.Provider[STORE,pop3s,com.sun.mail.pop3.POP3SSLStore,Oracle], smtp=javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle]}
DEBUG: successfully loaded resource: /META-INF/javamail.default.address.map
DEBUG: getProvider() returning javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle]
DEBUG SMTP: need username and password for authentication
DEBUG SMTP: protocolConnect returning false, host=smtp.exmail.qq.com, user=Administrator, password=<null>
DEBUG SMTP: useEhlo true, useAuth true
DEBUG SMTP: trying to connect to host "smtp.exmail.qq.com", port 465, isSSL false
DEBUG SMTP: EOF: [EOF]
DEBUG SMTP: could not connect to host "smtp.exmail.qq.com", port: 465, response: -1
问题二：配置了ssl参数，仍然报错535 Error: authentication failed, system busy
EHLO 20160314-172951
250-smtp.qq.com
250-PIPELINING
250-SIZE 73400320
250-AUTH LOGIN PLAIN
250-AUTH=LOGIN
250-MAILCOMPRESS
250 8BITMIME
DEBUG SMTP: Found extension "PIPELINING", arg ""
DEBUG SMTP: Found extension "SIZE", arg "73400320"
DEBUG SMTP: Found extension "AUTH", arg "LOGIN PLAIN"
DEBUG SMTP: Found extension "AUTH=LOGIN", arg ""
DEBUG SMTP: Found extension "MAILCOMPRESS", arg ""
DEBUG SMTP: Found extension "8BITMIME", arg ""
DEBUG SMTP: protocolConnect login, host=smtp.exmail.qq.com, user=*****@*****.com, password=<non-null>
DEBUG SMTP: Attempt to authenticate using mechanisms: LOGIN PLAIN DIGEST-MD5 NTLM XOAUTH2
DEBUG SMTP: Using mechanism LOGIN
DEBUG SMTP: AUTH LOGIN command trace suppressed
DEBUG SMTP: AUTH LOGIN failed
Exception in thread "main" javax.mail.AuthenticationFailedException: 535 Error: authentication failed, system busy
at com.sun.mail.smtp.SMTPTransport$Authenticator.authenticate(SMTPTransport.java:932)
at com.sun.mail.smtp.SMTPTransport.authenticate(SMTPTransport.java:843)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:748)
at javax.mail.Service.connect(Service.java:388)
at javax.mail.Service.connect(Service.java:246)
at javax.mail.Service.connect(Service.java:195)
at javax.mail.Transport.send0(Transport.java:254)
at javax.mail.Transport.send(Transport.java:124)
at com.jiuhou.common.util.mail.SimpleMailSender.sendTextMail(SimpleMailSender.java:55)
at com.jiuhou.common.util.mail.SimpleMailSender.main(SimpleMailSender.java:189)
问题分析和解决方案：
看日志，发现了一个关键点 LOGIN PLAIN DIGEST-MD5 NTLM XOAUTH2
有一个oauth2，这是常用于三方登录验证的一个标准，也就是说你的企业邮箱开启了譬如微信扫码登录验证的功能，如果开启了，很抱歉，只有通过三方认证才能成功登录企业邮箱，这就是authentication failed认证失败的原因。目前没有深入研究，还未找出通过三方认证的办法，但是有个解决办法可以用，就是关闭三方认证，这样就可以发邮件了。
备注：
另外说一个使用qq邮箱发邮件的问题，就是密码设置不是你的qq密码，而是开启smtp时给你的授权码，否则也发不了。