diff --git a/src/java/davmail/exchange/ExchangeSession.java b/src/java/davmail/exchange/ExchangeSession.java
index c6a6803d..7db9a757 100644
--- a/src/java/davmail/exchange/ExchangeSession.java
+++ b/src/java/davmail/exchange/ExchangeSession.java
@@ -227,8 +227,10 @@ public class ExchangeSession {
                 method = formLogin(httpClient, method, userName, password);
             }
 
-            // avoid 401 roundtrips
-            httpClient.getParams().setParameter(HttpClientParams.PREEMPTIVE_AUTHENTICATION, true);
+            // avoid 401 roundtrips, only if NTLM is disabled
+            if (!DavGatewayHttpClientFacade.hasNTLM(httpClient)) {
+                httpClient.getParams().setParameter(HttpClientParams.PREEMPTIVE_AUTHENTICATION, true);
+            }
 
             buildMailPath(method);
 
diff --git a/src/java/davmail/exchange/ExchangeSessionFactory.java b/src/java/davmail/exchange/ExchangeSessionFactory.java
index de5781d8..bb10e106 100644
--- a/src/java/davmail/exchange/ExchangeSessionFactory.java
+++ b/src/java/davmail/exchange/ExchangeSessionFactory.java
@@ -20,16 +20,16 @@ package davmail.exchange;
 
 import davmail.BundleMessage;
 import davmail.Settings;
-import davmail.exception.DavMailException;
 import davmail.exception.DavMailAuthenticationException;
+import davmail.exception.DavMailException;
 import davmail.http.DavGatewayHttpClientFacade;
 import org.apache.commons.httpclient.HttpClient;
-import org.apache.commons.httpclient.HttpMethod;
 import org.apache.commons.httpclient.HttpStatus;
 import org.apache.commons.httpclient.methods.GetMethod;
 
 import java.io.IOException;
-import java.net.*;
+import java.net.NetworkInterface;
+import java.net.SocketException;
 import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.Map;
@@ -124,6 +124,8 @@ public final class ExchangeSessionFactory {
             throw exc;
         } catch (DavMailException exc) {
             throw exc;
+        } catch (IllegalStateException exc) {
+            throw exc;
         } catch (Exception exc) {
             handleNetworkDown(exc);
         }
@@ -172,12 +174,11 @@ public final class ExchangeSessionFactory {
     public static void checkConfig() throws IOException {
         String url = Settings.getProperty("davmail.url");
         HttpClient httpClient = DavGatewayHttpClientFacade.getInstance();
-        HttpMethod testMethod = new GetMethod(url);
+        GetMethod testMethod = new GetMethod(url);
         try {
             // get webMail root url (will not follow redirects)
-            testMethod.setFollowRedirects(false);
             testMethod.setDoAuthentication(false);
-            int status = httpClient.executeMethod(testMethod);
+            int status = DavGatewayHttpClientFacade.executeGetMethod(httpClient, testMethod, false);
             ExchangeSession.LOGGER.debug("Test configuration status: " + status);
             if (status != HttpStatus.SC_OK && status != HttpStatus.SC_UNAUTHORIZED
                     && status != HttpStatus.SC_MOVED_TEMPORARILY && status != HttpStatus.SC_MOVED_PERMANENTLY) {
diff --git a/src/java/davmail/http/DavGatewayHttpClientFacade.java b/src/java/davmail/http/DavGatewayHttpClientFacade.java
index 2bbc5a07..af4ddb91 100644
--- a/src/java/davmail/http/DavGatewayHttpClientFacade.java
+++ b/src/java/davmail/http/DavGatewayHttpClientFacade.java
@@ -363,7 +363,12 @@ public final class DavGatewayHttpClientFacade {
         return status;
     }
 
-    private static boolean hasNTLM(HttpClient httpClient) {
+    /**
+     * Test if NTLM auth scheme is enabled.
+     * @param httpClient HttpClient instance
+     * @return true if NTLM is enabled
+     */
+    public static boolean hasNTLM(HttpClient httpClient) {
         Object authPrefs = httpClient.getParams().getParameter(AuthPolicy.AUTH_SCHEME_PRIORITY);
         return authPrefs instanceof List<?> && ((Collection) authPrefs).contains(AuthPolicy.NTLM);
     }
@@ -376,6 +381,19 @@ public final class DavGatewayHttpClientFacade {
         httpClient.getParams().setParameter(AuthPolicy.AUTH_SCHEME_PRIORITY, authPrefs);
     }
 
+    private static boolean acceptsNTLMOnly(GetMethod getMethod) {
+        Header authenticateHeader = null;
+        if (getMethod.getStatusCode() == HttpStatus.SC_UNAUTHORIZED) {
+            authenticateHeader = getMethod.getResponseHeader("Authenticate");
+        } else if (getMethod.getStatusCode() == HttpStatus.SC_PROXY_AUTHENTICATION_REQUIRED) {
+           authenticateHeader = getMethod.getResponseHeader("Proxy-Authenticate"); 
+        }
+        // check authenticate header
+        return (authenticateHeader != null)
+                && (authenticateHeader.getElements().length == 1)
+                && ("NTLM".equals(authenticateHeader.getElements()[0].getName()));
+    }
+
     /**
      * Execute Get method, do not follow redirects.
      *
@@ -383,18 +401,20 @@ public final class DavGatewayHttpClientFacade {
      * @param method          Http method
      * @param followRedirects Follow redirects flag
      * @throws IOException on error
+     * @return Http status
      */
-    public static void executeGetMethod(HttpClient httpClient, GetMethod method, boolean followRedirects) throws IOException {
+    public static int executeGetMethod(HttpClient httpClient, GetMethod method, boolean followRedirects) throws IOException {
         // do not follow redirects in expired sessions
         method.setFollowRedirects(followRedirects);
         int status = httpClient.executeMethod(method);
-        if (status == HttpStatus.SC_UNAUTHORIZED && !hasNTLM(httpClient)) {
+        if ((status == HttpStatus.SC_UNAUTHORIZED || status == HttpStatus.SC_PROXY_AUTHENTICATION_REQUIRED)
+                && acceptsNTLMOnly(method) && !hasNTLM(httpClient)) {
             method.releaseConnection();
-            LOGGER.debug("Received unauthorized at " + method.getURI() + ", retrying with NTLM");
+            LOGGER.debug("Received "+status+" unauthorized at " + method.getURI() + ", retrying with NTLM");
             addNTLM(httpClient);
             status = httpClient.executeMethod(method);
         }
-        if (status != HttpStatus.SC_OK) {
+        if (status != HttpStatus.SC_OK && (followRedirects || !isRedirect(status))) {
             LOGGER.warn("GET failed with status " + status + " at " + method.getURI() + ": " + method.getResponseBodyAsString());
             throw DavGatewayHttpClientFacade.buildHttpException(method);
         }
@@ -407,6 +427,7 @@ public final class DavGatewayHttpClientFacade {
                 throw DavGatewayHttpClientFacade.buildHttpException(method);
             }
         }
+        return status;
     }
 
     private static void checkExpiredSession(String queryString) throws DavMailAuthenticationException {