diff --git a/res/values/arrays.xml b/res/values/arrays.xml
index 70398b5..16e82fa 100755
--- a/res/values/arrays.xml
+++ b/res/values/arrays.xml
@@ -2,6 +2,7 @@
 <resources>
    
     <string-array name="check_intervals">
+        <item>5 sec</item>
         <item>15 sec</item>
         <item>30 sec</item>
         <item>1 minute</item>
@@ -14,6 +15,7 @@
     </string-array>
     
     <string-array name="check_intervals_values">
+        <item>5</item>
         <item>15</item>
         <item>30</item>
         <item>60</item>
diff --git a/src/org/envaya/sms/App.java b/src/org/envaya/sms/App.java
index 27f9305..100601a 100755
--- a/src/org/envaya/sms/App.java
+++ b/src/org/envaya/sms/App.java
@@ -99,6 +99,7 @@ public final class App extends Application {
     public static final int LOG_TIMESTAMP_INTERVAL = 60000; // ms
     
     public static final int HTTP_CONNECTION_TIMEOUT = 10000; // ms
+    public static final int HTTP_SOCKET_TIMEOUT = 60000; // ms
     
     // Each QueuedMessage is identified within our internal Map by its Uri.
     // Currently QueuedMessage instances are only available within EnvayaSMS,
@@ -353,14 +354,37 @@ public final class App extends Application {
                 extras);
     }
     
-    public void checkOutgoingMessages() 
+    private boolean pollActive = false;
+    private boolean requestedPoll = false;
+    
+    public synchronized void markPollComplete()
     {
-        String serverUrl = getServerUrl();
-        if (serverUrl.length() > 0) {
-            log("Checking for outgoing messages");
-            new PollerTask(this).execute();
-        } else {
-            log("Can't check outgoing messages; server URL not set");
+        pollActive = false;
+        
+        if (requestedPoll)
+        {
+            requestedPoll = false;
+            checkOutgoingMessages();
+        }
+    }
+    
+    public synchronized void checkOutgoingMessages() 
+    {
+        if (!pollActive)
+        {
+            String serverUrl = getServerUrl();
+            if (serverUrl.length() > 0) {
+                log("Checking for outgoing messages");
+                pollActive = true;
+                new PollerTask(this).execute();
+            } else {
+                log("Can't check outgoing messages; server URL not set");
+            }
+        }
+        else
+        {
+            debug("Waiting for server response...");
+            requestedPoll = true;
         }
     }
 
@@ -696,7 +720,7 @@ public final class App extends Application {
     {
         HttpParams httpParams = new BasicHttpParams();
         HttpConnectionParams.setConnectionTimeout(httpParams, HTTP_CONNECTION_TIMEOUT);
-        HttpConnectionParams.setSoTimeout(httpParams, HTTP_CONNECTION_TIMEOUT);                    
+        HttpConnectionParams.setSoTimeout(httpParams, HTTP_SOCKET_TIMEOUT);                    
         HttpProtocolParams.setContentCharset(httpParams, "UTF-8");            
         return httpParams;
     }
diff --git a/src/org/envaya/sms/Outbox.java b/src/org/envaya/sms/Outbox.java
index 2ec53f2..eb9929f 100755
--- a/src/org/envaya/sms/Outbox.java
+++ b/src/org/envaya/sms/Outbox.java
@@ -11,17 +11,27 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Comparator;
 import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
 import java.util.Map;
 import java.util.PriorityQueue;
+import java.util.Queue;
+import java.util.Set;
 import org.apache.http.message.BasicNameValuePair;
 import org.envaya.sms.receiver.DequeueOutgoingMessageReceiver;
 import org.envaya.sms.task.HttpTask;
 
 public class Outbox {
     private Map<Uri, OutgoingMessage> outgoingMessages = new HashMap<Uri, OutgoingMessage>();    
-
+    
     private App app;   
 
+    // keep track of some recent message URIs to avoid sending duplicate messages
+    // (e.g. if send_status HTTP request fails for some reason)
+    public static final int MAX_RECENT_URIS = 100;    
+    private Set<Uri> recentSentMessageUris = new HashSet<Uri>();
+    private Queue<Uri> recentSentMessageUriOrder = new LinkedList<Uri>();
+        
     // number of outgoing messages that are currently being sent and waiting for
     // messageSent or messageFailed to be called
     private int numSendingOutgoingMessages = 0;
@@ -108,7 +118,11 @@ public class Outbox {
         
         notifyMessageStatus(sms, App.STATUS_SENT, "");
         
-        outgoingMessages.remove(sms.getUri());
+        Uri uri = sms.getUri();
+        
+        outgoingMessages.remove(uri);
+        
+        addRecentSentMessage(sms);
         
         notifyChanged();
         
@@ -116,6 +130,23 @@ public class Outbox {
         maybeDequeueMessage();
     }
     
+    private synchronized void addRecentSentMessage(OutgoingMessage sms)
+    {        
+        if (sms.getServerId() != null)
+        {
+            Uri uri = sms.getUri();
+            
+            recentSentMessageUris.add(uri);            
+            recentSentMessageUriOrder.add(uri);
+            
+            if (recentSentMessageUriOrder.size() > MAX_RECENT_URIS)
+            {
+                Uri oldUri = recentSentMessageUriOrder.remove();
+                recentSentMessageUris.remove(oldUri);
+            }
+        }
+    }
+    
     public synchronized void messageFailed(OutgoingMessage sms, String error)
     {
         if (sms.scheduleRetry()) 
@@ -166,6 +197,13 @@ public class Outbox {
             app.debug("Duplicate outgoing " + sms.getLogName() + ", skipping");
             return;
         }
+        
+        if (recentSentMessageUris.contains(uri))
+        {
+            app.debug("Outgoing " + sms.getLogName() + " already sent, re-notifying server");   
+            notifyMessageStatus(sms, App.STATUS_SENT, "");
+            return;
+        }
 
         outgoingMessages.put(uri, sms);        
         enqueueMessage(sms);
diff --git a/src/org/envaya/sms/task/PollerTask.java b/src/org/envaya/sms/task/PollerTask.java
index 82f8644..6f20923 100755
--- a/src/org/envaya/sms/task/PollerTask.java
+++ b/src/org/envaya/sms/task/PollerTask.java
@@ -12,6 +12,12 @@ public class PollerTask extends HttpTask {
         super(app, new BasicNameValuePair("action", App.ACTION_OUTGOING));
     }
 
+    @Override
+    protected void onPostExecute(HttpResponse response) {
+        super.onPostExecute(response);
+        app.markPollComplete();
+    }
+    
     @Override
     protected void handleResponse(HttpResponse response) throws Exception {
         for (OutgoingMessage reply : parseResponseXML(response)) {