javax.mail.MessagingException: Connection dropped by server?;错误怎么解决

大家好，
我用javamail编写一个收邮件的软件，但是连接服务器时出现问题，出现以下提示错误（事先声明，地址，帐户，密码，端口都没有问题）邮箱服务器用的是microsoft exchange,谢谢:
javax.mail.MessagingException: Connection dropped by server?;
nested exception is:
java.io.IOException: Connection dropped by server?
at com.sun.mail.imap.IMAPStore.protocolConnect(IMAPStore.java:618)
at javax.mail.Service.connect(Service.java:291)
at Mails.Connexion.<init>(Connexion.java:38)
at Mails.Connexion.main(Connexion.java:68)
Caused by: java.io.IOException: Connection dropped by server?
at com.sun.mail.iap.ResponseInputStream.readResponse(ResponseInputStream.java:111)
at com.sun.mail.iap.Response.<init>(Response.java:91)
at com.sun.mail.imap.protocol.IMAPResponse.<init>(IMAPResponse.java:56)
at com.sun.mail.imap.protocol.IMAPResponse.readResponse(IMAPResponse.java:130)
at com.sun.mail.imap.protocol.IMAPProtocol.readResponse(IMAPProtocol.java:261)
at com.sun.mail.iap.Protocol.<init>(Protocol.java:116)
at com.sun.mail.imap.protocol.IMAPProtocol.<init>(IMAPProtocol.java:104)
at com.sun.mail.imap.IMAPStore.protocolConnect(IMAPStore.java:585)
... 3 more
我的程序:
private String host = "nmaimap.renault.fr";//l'adresse de l'hote
private String username = "corp\\V009732";//le login
private String password = "PSE2010";//le mot de passe
private String provider = "imap";//le protocole utilisé
private int port=993;
//private int port=25;
public Folder inbox;
public Store store;

public Connexion(){
Properties props = new Properties();
try {

// Connect to the server
Session session = Session.getDefaultInstance(props, null);
store = session.getStore(provider);
store.connect(host,port, username, password);
// Open the folder
inbox = store.getFolder("INBOX");
if (inbox == null) {
System.out.println("No INBOX");
System.exit(1);
}
inbox.open(Folder.READ_WRITE);

}catch (Exception e) {
//System.out.println("Connexion erreur");
e.printStackTrace();
}
}

//Déconnecter de la boite aux lettres, lancer à la fin de l'application
public final void deconexion(){
try{
// Close the connection
// but don't remove the messages from the server
inbox.close(true);
store.close();
}catch(Exception ex){
System.out.println("Connexion erreur");
}
}

public static void main(String[] args){
//pour tester la connextion
Connexion c=null;
c=new Connexion();//connecter en créant l'objet
c.deconexion();
}
谢谢大家指教