How to send external mail to the company mailbox server on the Intranet

The intranet mailbox configuration fails on the Internet

Alibaba cloud servers are used , After I deployed the system, I found that the email couldn't be sent, so I found out why Alibaba cloud server defaulted the email 25 The port is disabled in order to prevent mail flooding ,

It turns out that Ali has targeted 25 Ports are limited

Ali cloud, 《25 The port uses the service protocol 》：
I / Our company promises and guarantees TCP 25 The port is only used to connect to the third party SMTP The server , From a third party SMTP Server outgoing mail . If you are found using this machine IP direct SMTP Send E-mail , Have the right to permanently ban TCP 25 port , And no longer provide relevant services .

Go to the Alibaba cloud server background page to find 【 Safety control 】-【25 Port unsealed 】-【25 Port unsealing application 】 Fill in the information and wait for review .
Unable to find local direct resource customer service .

follow-up :
Public network 25 When you let it go , Still reporting a mistake , for example :SSLException: Unrecognized SSL message, plaintext connection?

Someone on the Internet said not to configure properties Inside
socketFactory Of class: javax.net.ssl.SSLSocketFactory,TSL The agreement is ordinary socker, This doesn't work
Then I was Delete the whole properties The configuration returns to normal , Just don't