diff --git a/meshms.c b/meshms.c
index ef8db671..9492d890 100644
--- a/meshms.c
+++ b/meshms.c
@@ -384,6 +384,51 @@ int app_meshms_list_messages(const struct cli_parsed *parsed, void *context)
  return 0;
 }
 
+
+int meshms_get_last_ack_offset(const char *left_sid,const char *right_sid)
+{
+  rhizome_manifest *m_left=NULL;
+  m_left=meshms_find_or_create_manifestid(left_sid,right_sid,0);
+  if (!m_left) {
+    DEBUGF("Couldn't find manifest for thread ply");
+    return 0;
+  }
+  unsigned char *left_messages=malloc(m_left->fileLength);
+  if (!left_messages) {
+    WHYF("malloc(%d) failed while reading meshms logs",m_left->fileLength);
+    return 0;
+  }
+  if (meshms_read_message(m_left,left_messages)) {
+    DEBUGF("Couldn't read message log for thread ply");
+    rhizome_manifest_free(m_left); return 0;
+  }
+
+  int left_len=m_left->fileLength;
+  rhizome_manifest_free(m_left); m_left=NULL;
+  
+  // Scan through messages and look for acks
+  int left_ack_limit=0;
+  int left_offset=0;
+  for(left_offset=0;left_offset<left_len;)
+    {
+      int block_type=meshms_block_type(left_messages,left_offset,left_len);
+      switch(block_type) {
+      case RHIZOME_MESHMS_BLOCK_TYPE_ACK:
+	{
+	  int o=left_offset;
+	  deserialize_ack(left_messages,&o,left_len,&left_ack_limit);
+	}
+	break;
+      }
+      unsigned int left_block_len;
+      int o=left_offset;
+      if (decode_length_forwards(left_messages,&o,left_len,&left_block_len)) break;     
+      left_offset+=left_block_len;
+    }
+  free(left_messages);
+  return left_ack_limit;
+}
+
 int app_meshms_ack_messages(const struct cli_parsed *parsed, void *context)
 {
  int ret = 0;
@@ -419,6 +464,13 @@ int app_meshms_ack_messages(const struct cli_parsed *parsed, void *context)
  if (recipient_sid[0] && str_to_sid_t(&aSid, recipient_sid) == -1)
    return WHYF("invalid recipient_sid: %s", recipient_sid);
 
+ DEBUGF("Message log previously acknowledged to %d",
+	meshms_get_last_ack_offset(sender_sid,recipient_sid));
+ if (meshms_get_last_ack_offset(sender_sid,recipient_sid)>=message_offset) {
+   INFO("Already acknowledged.");
+   return 0;
+ }
+
  // Create serialised ack message for appending to the conversation ply
  int length_int = 0;
  unsigned char buffer_serialize[100];
@@ -429,5 +481,7 @@ int app_meshms_ack_messages(const struct cli_parsed *parsed, void *context)
    ret|=meshms_append_messageblock(sender_sid,recipient_sid,
 				   buffer_serialize,length_int);
 
+ if (!ret) INFO("Acknowledged.");
+
  return ret;
 }