diff --git a/src/java/davmail/http/DavGatewayX509TrustManager.java b/src/java/davmail/http/DavGatewayX509TrustManager.java
index 1bd38df8..fa301054 100644
--- a/src/java/davmail/http/DavGatewayX509TrustManager.java
+++ b/src/java/davmail/http/DavGatewayX509TrustManager.java
@@ -8,13 +8,14 @@ import javax.net.ssl.TrustManager;
 import javax.net.ssl.TrustManagerFactory;
 import javax.net.ssl.X509TrustManager;
 import java.awt.*;
-import java.security.KeyStore;
-import java.security.KeyStoreException;
-import java.security.MessageDigest;
-import java.security.NoSuchAlgorithmException;
+import java.security.*;
 import java.security.cert.CertificateEncodingException;
 import java.security.cert.CertificateException;
 import java.security.cert.X509Certificate;
+import java.text.SimpleDateFormat;
+import java.io.IOException;
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
 
 /**
  * Custom Trust Manager, let user accept or deny.
@@ -56,31 +57,90 @@ public class DavGatewayX509TrustManager implements X509TrustManager {
     }
 
     protected void userCheckServerTrusted(final X509Certificate[] x509Certificates) throws CertificateException {
-        try {
-            String acceptedCertificateHash = Settings.getProperty("davmail.server.certificate.hash");
-            String certificateHash = getFormattedHash(x509Certificates[0]);
-            // if user already accepted a certificate,
-            if (acceptedCertificateHash != null && acceptedCertificateHash.length() > 0
-                    && acceptedCertificateHash.equals(certificateHash)) {
-                DavGatewayTray.debug("Found permanently accepted certificate, hash " + acceptedCertificateHash);
+        String acceptedCertificateHash = Settings.getProperty("davmail.server.certificate.hash");
+        String certificateHash = getFormattedHash(x509Certificates[0]);
+        // if user already accepted a certificate,
+        if (acceptedCertificateHash != null && acceptedCertificateHash.length() > 0
+                && acceptedCertificateHash.equals(certificateHash)) {
+            DavGatewayTray.debug("Found permanently accepted certificate, hash " + acceptedCertificateHash);
+        } else {
+            boolean isCertificateTrusted;
+            if (Settings.getBooleanProperty("davmail.server")) {
+                // headless mode
+                isCertificateTrusted = isCertificateTrusted(x509Certificates[0]);
             } else {
-
-                if (!AcceptCertificateDialog.isCertificateTrusted(x509Certificates[0])) {
-                    throw new CertificateException("User rejected certificate");
-                }
-                // certificate accepted, store in settings
-                Settings.saveProperty("davmail.server.certificate.hash", certificateHash);
+                isCertificateTrusted = AcceptCertificateDialog.isCertificateTrusted(x509Certificates[0]);
             }
-        } catch (NoSuchAlgorithmException nsa) {
-            throw new CertificateException(nsa);
+            if (!isCertificateTrusted) {
+                throw new CertificateException("User rejected certificate");
+            }
+            // certificate accepted, store in settings
+            Settings.saveProperty("davmail.server.certificate.hash", certificateHash);
         }
     }
 
-    public static String getFormattedHash(X509Certificate certificate) throws NoSuchAlgorithmException, CertificateEncodingException {
+    protected boolean isCertificateTrusted(X509Certificate certificate) {
+        BufferedReader inReader = new BufferedReader(new InputStreamReader(System.in));
+        String answer = null;
+        while (!"y".equals(answer) && !"Y".equals(answer) && !"n".equals(answer) && !"N".equals(answer) ) {
+            System.out.println("Server Certificate:");
+            System.out.println("Issued to: " + DavGatewayX509TrustManager.getRDN(certificate.getSubjectDN()));
+            System.out.println("Issued by: " + getRDN(certificate.getIssuerDN()));
+            SimpleDateFormat formatter = new SimpleDateFormat("MM/dd/yyyy");
+            String notBefore = formatter.format(certificate.getNotBefore());
+            System.out.println("Valid from: " + notBefore);
+            String notAfter = formatter.format(certificate.getNotAfter());
+            System.out.println("Valid until: " + notAfter);
+            System.out.println("Serial: " + getFormattedSerial(certificate));
+            String sha1Hash = DavGatewayX509TrustManager.getFormattedHash(certificate);
+            System.out.println("FingerPrint: " + sha1Hash);
+            System.out.println();
+            System.out.println("Server provided an untrusted certificate,");
+            System.out.println("you can choose to accept or deny access.");
+            System.out.println("Accept certificate (y/n)?");
+            try {
+                answer = inReader.readLine();
+            } catch (IOException e) {
+                System.err.println(e);
+            }
+        }
+        return "y".equals(answer) || "Y".equals(answer);
+    }
+
+    public static String getRDN(Principal principal) {
+        String dn = principal.getName();
+        int start = dn.indexOf('=');
+        int end = dn.indexOf(',');
+        if (start >= 0 && end >= 0) {
+            return dn.substring(start + 1, end);
+        } else {
+            return dn;
+        }
+    }
+
+    public static String getFormattedSerial(X509Certificate certificate) {
+        StringBuilder builder = new StringBuilder();
+        String serial = certificate.getSerialNumber().toString(16);
+        for (int i = 0; i < serial.length(); i++) {
+            if (i > 0 && i % 2 == 0) {
+                builder.append(' ');
+            }
+            builder.append(serial.charAt(i));
+        }
+        return builder.toString().toUpperCase();
+    }
+
+    public static String getFormattedHash(X509Certificate certificate) {
         String sha1Hash;
-        MessageDigest md = MessageDigest.getInstance("SHA1");
-        byte[] digest = md.digest(certificate.getEncoded());
-        sha1Hash = formatHash(digest);
+        try {
+            MessageDigest md = MessageDigest.getInstance("SHA1");
+            byte[] digest = md.digest(certificate.getEncoded());
+            sha1Hash = formatHash(digest);
+        } catch (NoSuchAlgorithmException nsa) {
+            sha1Hash = nsa.getMessage();
+        } catch (CertificateEncodingException cee) {
+            sha1Hash = cee.getMessage();
+        }
         return sha1Hash;
     }
 
diff --git a/src/java/davmail/ui/AcceptCertificateDialog.java b/src/java/davmail/ui/AcceptCertificateDialog.java
index 8517ca85..813ca42a 100644
--- a/src/java/davmail/ui/AcceptCertificateDialog.java
+++ b/src/java/davmail/ui/AcceptCertificateDialog.java
@@ -36,39 +36,9 @@ public class AcceptCertificateDialog extends JDialog {
         panel.add(fieldPanel);
     }
 
-    protected String getRDN(Principal principal) {
-        String dn = principal.getName();
-        int start = dn.indexOf('=');
-        int end = dn.indexOf(',');
-        if (start >= 0 && end >= 0) {
-            return dn.substring(start + 1, end);
-        } else {
-            return dn;
-        }
-    }
-
-    public String getFormattedSerial(X509Certificate certificate) {
-        StringBuilder builder = new StringBuilder();
-        String serial = certificate.getSerialNumber().toString(16);
-        for (int i = 0; i < serial.length(); i++) {
-            if (i > 0 && i % 2 == 0) {
-                builder.append(' ');
-            }
-            builder.append(serial.charAt(i));
-        }
-        return builder.toString().toUpperCase();
-    }
-
     public AcceptCertificateDialog(X509Certificate certificate) {
         setAlwaysOnTop(true);
-        String sha1Hash;
-        try {
-            sha1Hash = DavGatewayX509TrustManager.getFormattedHash(certificate);
-        } catch (NoSuchAlgorithmException nsa) {
-            sha1Hash = nsa.getMessage();
-        } catch (CertificateEncodingException cee) {
-            sha1Hash = cee.getMessage();
-        }
+        String sha1Hash = DavGatewayX509TrustManager.getFormattedHash(certificate);
         SimpleDateFormat formatter = new SimpleDateFormat("MM/dd/yyyy");
 
         setTitle("DavMail: Accept certificate ?");
@@ -81,8 +51,8 @@ public class AcceptCertificateDialog extends JDialog {
         JPanel subjectPanel = new JPanel();
         subjectPanel.setLayout(new BoxLayout(subjectPanel, BoxLayout.Y_AXIS));
         subjectPanel.setBorder(BorderFactory.createTitledBorder("Server Certificate"));
-        addFieldValue(subjectPanel, "Issued to", getRDN(certificate.getSubjectDN()));
-        addFieldValue(subjectPanel, "Issued by", getRDN(certificate.getIssuerDN()));
+        addFieldValue(subjectPanel, "Issued to", DavGatewayX509TrustManager.getRDN(certificate.getSubjectDN()));
+        addFieldValue(subjectPanel, "Issued by", DavGatewayX509TrustManager.getRDN(certificate.getIssuerDN()));
         Date now = new Date();
         String notBefore = formatter.format(certificate.getNotBefore());
         if (now.before(certificate.getNotBefore())) {
@@ -94,7 +64,7 @@ public class AcceptCertificateDialog extends JDialog {
            notAfter = "<html><font color=\"#FF0000\">"+notAfter+"</font></html>";
         }
         addFieldValue(subjectPanel, "Valid until", notAfter);
-        addFieldValue(subjectPanel, "Serial", getFormattedSerial(certificate));
+        addFieldValue(subjectPanel, "Serial", DavGatewayX509TrustManager.getFormattedSerial(certificate));
         addFieldValue(subjectPanel, "FingerPrint", sha1Hash);
 
         JPanel warningPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));