diff --git a/mozilla/mailnews/compose/resources/content/MsgComposeCommands.js b/mozilla/mailnews/compose/resources/content/MsgComposeCommands.js
index 459be3bf479..d2690ccdf21 100644
--- a/mozilla/mailnews/compose/resources/content/MsgComposeCommands.js
+++ b/mozilla/mailnews/compose/resources/content/MsgComposeCommands.js
@@ -1866,8 +1866,19 @@ function LoadIdentity(startup)
             try {
               serverURL.spec = prefs.CopyCharPref(autocompleteDirectory + ".uri");
             } catch (ex) {dump("ERROR: " + ex + "\n");}
-            dump("url is " +  serverURL.spec +"\n");
             session2.serverURL = serverURL;
+
+            // don't search on strings shorter than this
+            //
+            try { 
+                session2.minStringLength = 
+                    prefs.GetIntPref(autocompleteDirectory + 
+                                     ".autoComplete.minStringLength");
+            } catch (ex) {
+                // if this pref isn't there, no big deal.  just let
+                // nsLDAPAutoCompleteSession use its default.
+            }
+
             session2.filterTemplate = "cn=";
             session2.outputFormat = "cn <mail>";
             session2.sizeLimit = 10;
diff --git a/mozilla/xpfe/components/autocomplete/public/nsILDAPAutoCompleteSession.idl b/mozilla/xpfe/components/autocomplete/public/nsILDAPAutoCompleteSession.idl
index 49c34aa8042..8e32fb81c9a 100644
--- a/mozilla/xpfe/components/autocomplete/public/nsILDAPAutoCompleteSession.idl
+++ b/mozilla/xpfe/components/autocomplete/public/nsILDAPAutoCompleteSession.idl
@@ -62,6 +62,18 @@ interface nsILDAPAutoCompleteSession : nsIAutoCompleteSession {
      */
     attribute long sizeLimit;
 
+    /**
+     * Strings shorter than this will return |nsIAutoCompleteStatus::ignored|
+     * rather than triggering a search.  This allows browsers to be
+     * configured to not search on substrings so short that they
+     * aren't indexed by the LDAP server (such searches can use significantly 
+     * more server resources and return a very large number of entries).
+     * The default is 0, meaning that no such limit is in effect.
+     * 
+     * @exception NS_ERROR_NULL_POINTER  NULL pointer passed to getter
+     */
+    attribute unsigned long minStringLength;
+
     /**
      * LDAP server to complete against, in ldap: URL format.  
      * May change to an nsILDAPServer once that infrastructure lands.
diff --git a/mozilla/xpfe/components/autocomplete/src/nsLDAPAutoCompleteSession.cpp b/mozilla/xpfe/components/autocomplete/src/nsLDAPAutoCompleteSession.cpp
index 959278ce1b6..4990c9ead44 100644
--- a/mozilla/xpfe/components/autocomplete/src/nsLDAPAutoCompleteSession.cpp
+++ b/mozilla/xpfe/components/autocomplete/src/nsLDAPAutoCompleteSession.cpp
@@ -50,7 +50,7 @@ NS_IMPL_ISUPPORTS3(nsLDAPAutoCompleteSession, nsIAutoCompleteSession,
                    nsILDAPMessageListener, nsILDAPAutoCompleteSession)
 
 nsLDAPAutoCompleteSession::nsLDAPAutoCompleteSession() :
-    mState(UNBOUND)
+    mState(UNBOUND), mMinStringLength(0)
 {
     NS_INIT_ISUPPORTS();
 }
@@ -89,11 +89,13 @@ nsLDAPAutoCompleteSession::OnStartLookup(const PRUnichar *searchString,
         mListener = listener;   // save it for later callbacks
     }
 
-    // ignore the empty string and strings with @ in them
+    // ignore the empty string, strings with @ in them, and strings
+    // that are too short
     //
-    if (searchString[0] == 0 || 
-        nsLiteralString(searchString).FindChar(PRUnichar('@'), 0) 
-        != kNotFound) {
+    if (searchString[0] == 0 ||
+        nsLiteralString(searchString).FindChar(PRUnichar('@'), 0) != 
+        kNotFound || 
+        mMinStringLength && nsCRT::strlen(searchString) < mMinStringLength)  {
 
         FinishAutoCompleteLookup(nsIAutoCompleteStatus::ignored);
         return NS_OK;
@@ -1028,4 +1030,24 @@ nsLDAPAutoCompleteSession::SetServerURL(nsILDAPURL * aServerURL)
     return NS_OK;
 }
 
+// attribute unsigned long minStringLength
+NS_IMETHODIMP
+nsLDAPAutoCompleteSession::GetMinStringLength(PRUint32 *aMinStringLength)
+{
+    if (!aMinStringLength) {
+        return NS_ERROR_NULL_POINTER;
+    }
+
+    *aMinStringLength = mMinStringLength;
+    return NS_OK;
+}
+NS_IMETHODIMP
+nsLDAPAutoCompleteSession::SetMinStringLength(PRUint32 aMinStringLength)
+{
+    mMinStringLength = aMinStringLength;
+
+    return NS_OK;
+}
+
+
 #endif
diff --git a/mozilla/xpfe/components/autocomplete/src/nsLDAPAutoCompleteSession.h b/mozilla/xpfe/components/autocomplete/src/nsLDAPAutoCompleteSession.h
index 78b979289e8..1c0fd535707 100644
--- a/mozilla/xpfe/components/autocomplete/src/nsLDAPAutoCompleteSession.h
+++ b/mozilla/xpfe/components/autocomplete/src/nsLDAPAutoCompleteSession.h
@@ -61,7 +61,7 @@ class nsLDAPAutoCompleteSession : public nsILDAPMessageListener,
     nsString mOutputFormat;                       // how to format output
     nsCOMPtr<nsILDAPURL> mServerURL;        // URL for the directory to search
     PRInt32 mSizeLimit;                     // return at most this many entries
-
+    PRUint32 mMinStringLength;              // strings < this size are ignored
 
     // stopgap until nsLDAPService works
     nsresult InitConnection();