Thanks your advice but I upgrade both elasticsearch and watcher to 2.0.0（without rc1, sure）, it still gives:
[2015-10-29 16:25:02,004][ERROR][watcher.actions.email ] [crawler_service_001] failed to execute action [error-watch/alert_email]
javax.mail.MessagingException: failed to send email with subject [errors encountered!] via account [u51_account];
nested exception is:
javax.mail.MessagingException: IOException while sending message;
nested exception is:
javax.activation.UnsupportedDataTypeException: no object DCH for MIME type multipart/mixed;
boundary="----=_Part_4_1547992646.1446107101838"
at org.elasticsearch.watcher.actions.email.service.InternalEmailService.send(InternalEmailService.java:85)
at org.elasticsearch.watcher.actions.email.service.InternalEmailService.send(InternalEmailService.java:77)
at org.elasticsearch.watcher.actions.email.ExecutableEmailAction.execute(ExecutableEmailAction.java:67)
at org.elasticsearch.watcher.actions.ActionWrapper.execute(ActionWrapper.java:106)
at org.elasticsearch.watcher.execution.ExecutionService.executeInner(ExecutionService.java:381)
at org.elasticsearch.watcher.execution.ExecutionService.execute(ExecutionService.java:274)
at org.elasticsearch.watcher.execution.ExecutionService$WatchExecutionTask.run(ExecutionService.java:419)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: javax.mail.MessagingException: IOException while sending message;
nested exception is:
javax.activation.UnsupportedDataTypeException: no object DCH for MIME type multipart/mixed;
boundary="----=_Part_4_1547992646.1446107101838"
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1245)
at org.elasticsearch.watcher.actions.email.service.Account.send(Account.java:109)
at org.elasticsearch.watcher.actions.email.service.InternalEmailService.send(InternalEmailService.java:83)
... 9 more
Caused by: javax.activation.UnsupportedDataTypeException: no object DCH for MIME type multipart/mixed;
boundary="----=_Part_4_1547992646.1446107101838"
at javax.activation.ObjectDataContentHandler.writeTo(DataHandler.java:896)
at javax.activation.DataHandler.writeTo(DataHandler.java:317)
at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:1627)
at javax.mail.internet.MimeMessage.writeTo(MimeMessage.java:1849)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1196)
... 11 more