diff --git a/main.py b/main.py
index ae50a5d..771dc61 100644
--- a/main.py
+++ b/main.py
@@ -2,13 +2,14 @@
 """TeamPulse — Teams meeting chat audit tool.
 
 Usage:
-    .venv/bin/python main.py [meeting-url]
+    .venv/bin/python main.py [--history]
+
+--history   Auch bestehende Chat-Nachrichten auswerten (Standard: nur neue ab Scriptstart)
 
-If no URL is given, the clipboard is checked for a Teams meeting link.
-If neither yields a URL, navigate manually in the browser window.
 Post !start "Presenter Name" and !stop in the chat to define a time window.
 A Markdown memo is saved to the current directory when the window closes.
 """
+import argparse
 import platform
 import re
 import subprocess
@@ -69,6 +70,15 @@ def _get_meeting_url() -> str | None:
 
 
 def main():
+    parser = argparse.ArgumentParser(description="TeamPulse — Teams Chat Auswertung")
+    parser.add_argument(
+        "--history",
+        action="store_true",
+        help="Bestehende Nachrichten auswerten (Standard: nur neue ab Scriptstart)",
+    )
+    args = parser.parse_args()
+    include_history: bool = args.history
+
     meeting_url = _get_meeting_url()
 
     with sync_playwright() as playwright:
@@ -109,7 +119,7 @@ def main():
         resolver = Resolver(cache_path=CACHE_PATH, page=page)
 
         while True:
-            window = monitor.run_once()
+            window = monitor.run_once(skip_existing=not include_history)
 
             print(f"\nLöse {len(window.entries)} E-Mail-Adresse(n) auf...")
             resolved_entries = []
diff --git a/src/teampulse/monitor.py b/src/teampulse/monitor.py
index add614e..8acc10b 100644
--- a/src/teampulse/monitor.py
+++ b/src/teampulse/monitor.py
@@ -151,16 +151,17 @@ class Monitor:
                 ))
         return new_messages
 
-    def run_once(self) -> AuditWindow:
+    def run_once(self, skip_existing: bool = True) -> AuditWindow:
         import time
 
         self.wait_for_chat()
 
-        # Bestehende Nachrichten als "gesehen" markieren — nur neue ab jetzt zählen
-        try:
-            self.poll_new_messages()
-        except Exception:
-            pass
+        if skip_existing:
+            # Bestehende Nachrichten als "gesehen" markieren — nur neue ab jetzt zählen
+            try:
+                self.poll_new_messages()
+            except Exception:
+                pass
 
         presenter: str | None = None
         start_time: datetime | None = None