JavaMail 发送邮件出现 Connection reset 问题

问题描述

使用 java mail 发送邮件的时候，申请的 163 邮箱作为发件箱，然无论如何配置，均出现 Connection reset，无法正常发送邮件。

Exception in thread "pool-2-thread-1" cn.hutool.extra.mail.MailException: MessagingException: Could not connect to SMTP host: smtp.163.com, port: 465
	at cn.hutool.extra.mail.Mail.send(Mail.java:229)
	at cn.hutool.extra.mail.MailUtil.send(MailUtil.java:211)
	at cn.hutool.extra.mail.MailUtil.send(MailUtil.java:175)
	at com.shulipeng.common.service.impl.MailServiceImpl.sendMail(MailServiceImpl.java:57)
	at com.shulipeng.activiti.listener.MyEventListener.sendMail(MyEventListener.java:134)
	at com.shulipeng.activiti.listener.MyEventListener.lambda$notify$0(MyEventListener.java:93)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: javax.mail.MessagingException: Could not connect to SMTP host: smtp.163.com, port: 465;
  nested exception is:
	java.net.SocketException: Connection reset
	at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2211)
	at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:740)
	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 cn.hutool.extra.mail.Mail.doSend(Mail.java:241)
	at cn.hutool.extra.mail.Mail.send(Mail.java:227)
	... 8 more
Caused by: java.net.SocketException: Connection reset
	at java.net.SocketInputStream.read(SocketInputStream.java:210)
	at java.net.SocketInputStream.read(SocketInputStream.java:141)
	at sun.security.ssl.InputRecord.readFully(InputRecord.java:465)
	at sun.security.ssl.InputRecord.read(InputRecord.java:503)
	at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:975)
	at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1367)
	at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1395)
	at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1379)
	at com.sun.mail.util.SocketFetcher.configureSSLSocket(SocketFetcher.java:620)
	at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:394)
	at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:218)
	at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:2175)
	... 16 more

问题解决

相同的代码，用公司的网络不能正常发送，用自己手机发出来的热点可以发送，原因是因为被墙了😓....
由于是公司电脑进行开发，是处于内网状态，虽然我们去 telnet smtp.163.com 25 或者 telnet smtp.163.com 465 都是通的，
但由于发送邮件的时候是通过 socket 与邮箱服务器进行通信的，由于防火墙的原因，导致着邮箱服务器和自己的电脑连接失败，所以出现此问题。