[Java Mail] com.sun.mail.smtp.SMTPSendFailedException: 452 message processing failed: connection timeout

Problem
I am using JavaMail to send email. But I got this error message as bellows:

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DEBUG SMTP: MessagingException while sending, THROW: com.sun.mail.smtp.SMTPSendFailedException: 452 message processing failed: connection timeout at com.sun.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:2203) at com.sun.mail.smtp.SMTPTransport.finishData(SMTPTransport.java:1981) at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1197) at org.springframework.mail.javamail.JavaMailSenderImpl.doSend(JavaMailSenderImpl.java:448) at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:345) at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:340) at com.yuantalife.ecp.commons.service.EmailService.send(EmailService.java:260)

How-to
This is not program's problem. This error may resulted from SMTP server. 
It may :

1. The ISP server’s disk system has run out of storage space, so the action had to be cancelled.
2. Most ISPs mail servers impose a maximum number of concurrent connections that client’s mail servers can attempt to make, and they usually also have a limit on the number of messages that are sent per connection.
3. This error can also be indicative of a problem on your own mail server. ex. out of memory.

Reference
[1] http://www.answersthatwork.com/Download_Area/ATW_Library/Networking/Network__3-SMTP_Server_Status_Codes_and_SMTP_Error_Codes.pdf