Please help us to resolve following issue urgently.

We are getting following exception while sending mails through our java application. Sometimes mail are going but many times we  are  getting  different types of exceptions

javax.mail.MessagingException: Can't send command to SMTP host;

  nested exception is:

java.net.SocketException: Connection closed by remote host

at com.sun.mail.smtp.SMTPTransport.sendCommand(SMTPTransport.java:2324)

at com.sun.mail.smtp.SMTPTransport.sendCommand(SMTPTransport.java:2311)

at com.sun.mail.smtp.SMTPTransport.issueCommand(SMTPTransport.java:2227)

at com.sun.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:2264)

at com.sun.mail.smtp.SMTPTransport.mailFrom(SMTPTransport.java:1758)

at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1257)

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Email configuration are as follows