imap plugin continued read a lot of repeat email

[sunyaxiong]

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For all general issues, please provide the following details for fast resolution:

• Version:7.8.0
• Operating System: CentO S
• Config File (if you have sensitive info, please remove it):
  '''
  input {
  imap {
  host => "imap.host.com"
  user => "[email protected]"
  password => "mypasswd"
  content_type => "text/plain"
  secure => true
  port => 993
  check_interval => 10
  folder => "Inbox"
  }
  }

output {
stdout { codec => rubydebug }

elasticsearch {
	index => "emails"
	document_type => "_doc"
	hosts => "172.31.27.212:9200"
	user => "elastic"
	password => "mypasswd"
}

}
'''

• Sample Data: None
• Steps to Reproduce:
  1: ./bin/logstash -f logstash.conf`，run the logstash and monitoring the mail server
  2: send a test email to mail address
  3: logstash consle print the email info and continue print the same email. meantime, elasticsearch recived many repeat email.