发送邮件时遇到的问题！

发送邮件时遇到的问题，如下，是循环发送邮件，有时候发送成功，不成功会抛出以下信息。大家帮忙看看
org.springframework.mail.MailSendException: Mail server connection failed; nested exception is javax.mail.MessagingException: Could not connect to SMTP host: 211.152.45.108, port: 25, response: 554
javax.mail.MessagingException: Could not connect to SMTP host: 211.152.45.108, port: 25, response: 554
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1215)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:322)
at javax.mail.Service.connect(Service.java:236)
at org.springframework.mail.javamail.JavaMailSenderImpl.doSend(JavaMailSenderImpl.java:373)
at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:291)
at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:277)
at com.sbtic.igg.util.MailSender2.sendMail(MailSender2.java:62)
at com.sbtic.igg.util.MailSender2.run(MailSender2.java:47)
at java.lang.Thread.run(Thread.java:595)