diff --git a/source/Form1.cs b/source/Form1.cs
index 9d68c75..3ec7c04 100644
--- a/source/Form1.cs
+++ b/source/Form1.cs
@@ -827,11 +827,13 @@ private void btn_read_Outlook_Click(object sender, EventArgs e)
             // check whether the user had the shift key pressed while calling this function and store this in a variable for further use
             bool shiftpressed_for_custom_folder = false;
             bool ctrlpressed_for_category_filter = false;
+            bool altpressed_for_category_exclusion_filter = false;
 
             if ((Control.ModifierKeys & Keys.Shift) == Keys.Shift) { shiftpressed_for_custom_folder = true; }
             if ((Control.ModifierKeys & Keys.Control) == Keys.Control) { ctrlpressed_for_category_filter = true; }
+            if ((Control.ModifierKeys & Keys.Alt) == Keys.Alt) { altpressed_for_category_exclusion_filter = true; }
 
-            ReadDataReturn myReadDataReturn = read_data_Outlook(shiftpressed_for_custom_folder, ctrlpressed_for_category_filter);
+            ReadDataReturn myReadDataReturn = read_data_Outlook(shiftpressed_for_custom_folder, ctrlpressed_for_category_filter, altpressed_for_category_exclusion_filter);
 
             if (myReadDataReturn.duplicates != "") MessageBox.Show(myReadDataReturn.duplicates, "The following duplicate entries could not be imported");
             update_datagrid();
@@ -1005,7 +1007,8 @@ private bool CheckOutlookVersion(string OL_version)
 
         }
 
-        private ReadDataReturn read_data_Outlook(bool customfolder, bool categoryfilter)
+        private ReadDataReturn read_data_Outlook(bool customfolder, bool categoryfilter,
+            bool categoryExclusionFilter)
         {
             // read all information from Outlook and save all contacts that have at least one phone or fax number
 
@@ -1047,10 +1050,21 @@ private ReadDataReturn read_data_Outlook(bool customfolder, bool categoryfilter)
             string my_category_filter = "";
             if (categoryfilter == true)
             {
-                SimpleInputDialog MySimpleInputDialog = new SimpleInputDialog("Please enter the string that must be present in the category field:", "Category Filter", false, false);
-                MySimpleInputDialog.ShowDialog();
-                my_category_filter = MySimpleInputDialog.resultstring;
-                MySimpleInputDialog.Dispose();
+                using (SimpleInputDialog mySimpleInputDialog = new SimpleInputDialog("Please enter the string that must be present in the category field:", "Category Filter", false, false))
+                {
+                    mySimpleInputDialog.ShowDialog();
+                    my_category_filter = mySimpleInputDialog.resultstring;
+                }
+            }
+
+            string my_category_exclusion_filter = "";
+            if (categoryExclusionFilter == true)
+            {
+                using (SimpleInputDialog mySimpleInputDialog = new SimpleInputDialog("Please enter the string that must *not* be present in the category field:", "Category Filter", false, false))
+                {
+                    mySimpleInputDialog.ShowDialog();
+                    my_category_exclusion_filter = mySimpleInputDialog.resultstring;
+                }
             }
 
             Microsoft.Office.Interop.Outlook.Items oContactItems = outlookFolder.Items;
@@ -1088,6 +1102,12 @@ private ReadDataReturn read_data_Outlook(bool customfolder, bool categoryfilter)
                     continue;   // abort this foreach loop and switch to the next contact
                 }
 
+                // if a category exclusion filter has been selected, we now check this first in order to save time (we can skip the contact data transfer if the excluded category is present)
+                if (my_category_exclusion_filter != "" && categories.Contains(my_category_exclusion_filter))
+                {
+                    continue;
+                }
+
                 GroupDataContact myContact = new GroupDataContact();
                 myContact.lastname = (myContactItem.LastName == null) ? string.Empty : myContactItem.LastName;
                 myContact.firstname = (myContactItem.FirstName == null) ? string.Empty : myContactItem.FirstName;