diff --git a/mozilla/mailnews/compose/resources/content/MsgComposeCommands.js b/mozilla/mailnews/compose/resources/content/MsgComposeCommands.js
index f2f768bbe6c..5d41ebe29a4 100644
--- a/mozilla/mailnews/compose/resources/content/MsgComposeCommands.js
+++ b/mozilla/mailnews/compose/resources/content/MsgComposeCommands.js
@@ -2543,6 +2543,10 @@ function LoadIdentity(startup)
           try {
             gMsgCompose.SetSignature(gCurrentIdentity);
           } catch (ex) { dump("### Cannot set the signature: " + ex + "\n");}
+
+          var event = document.createEvent('Events');
+          event.initEvent('compose-from-changed', false, true);
+          document.getElementById("msgcomposeWindow").dispatchEvent(event);
         }
 
       AddDirectoryServerObserver(false);
diff --git a/mozilla/mailnews/extensions/smime/resources/content/msgCompSMIMEOverlay.js b/mozilla/mailnews/extensions/smime/resources/content/msgCompSMIMEOverlay.js
index b0ae1acba02..443981a0173 100644
--- a/mozilla/mailnews/extensions/smime/resources/content/msgCompSMIMEOverlay.js
+++ b/mozilla/mailnews/extensions/smime/resources/content/msgCompSMIMEOverlay.js
@@ -383,7 +383,43 @@ function onComposerSendMessage()
   }
 }
 
+function onComposerFromChanged()
+{
+  if (!gSMFields)
+    return;
+
+  // In order to provide maximum protection to the user:
+  // - If encryption is already enabled, we will not turn it off automatically.
+  // - If encryption is not enabled, but the new account defaults to encryption, we will turn it on.
+  // - If signing is disabled, we will not turn it on automatically.
+  // - If signing is enabled, but the new account defaults to not sign, we will turn signing off.
+
+  if (!gSMFields.requireEncryptMessage)
+  {
+    var encryptionPolicy = gCurrentIdentity.getIntAttribute("encryptionpolicy");
+    // 0 == never, 1 == if possible, 2 == always Encrypt.
+
+    if (encryptionPolicy == 2)
+    {
+      gSMFields.requireEncryptMessage = true;
+      setEncryptionUI();
+    }
+  }
+
+  if (gSMFields.signMessage)
+  {
+    var signMessage = gCurrentIdentity.getBoolAttribute("sign_mail");
+    
+    if (!signMessage)
+    {
+      gSMFields.signMessage = false;
+      setNoSignatureUI();
+    }
+  }
+}
+
 top.controllers.appendController(SecurityController);
 addEventListener('compose-window-close', onComposerClose, true);
 addEventListener('compose-window-reopen', onComposerReOpen, true);
 addEventListener('compose-send-message', onComposerSendMessage, true);
+addEventListener('compose-from-changed', onComposerFromChanged, true);