The following Groovy code connects to an IMAP mailbox and read all unread messages.

import javax.mail.*
import javax.mail.search.*
import java.util.Properties

Properties props = new Properties()
props.setProperty("mail.store.protocol", "imap")
props.setProperty("mail.imap.host", host)
props.setProperty("mail.imap.port", port)
def session = Session.getDefaultInstance(props, null)
def store = session.getStore("imap")
def inbox

try {
  store.connect(host, username, password)
  inbox = openFolder(store, "INBOX")
  def messages = inbox.search(
    new FlagTerm(new Flags(Flags.Flag.DELETED), false))
  messages.each { msg ->
    println("${msg.subject} ${msg.sender}")
    msg.setFlag(Flags.Flag.SEEN, true)
  }
} finally {
  if(inbox) {
    inbox.close(true)
  }
  store.close()
}