diff --git a/src/clear_bookings.py b/src/clear_bookings.py
index a84fb72..f66328c 100644
--- a/src/clear_bookings.py
+++ b/src/clear_bookings.py
@@ -10,7 +10,7 @@ import ssl
 from datetime import datetime, date, timedelta
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
-from email.utils import format_datetime
+from email.utils import format_datetime, make_msgid
 from pathlib import Path
 
 import caldav
@@ -618,8 +618,11 @@ def send_mail_to_organizer(
 
     recipients = [recipient]
 
+    sender_domain = os.getenv('SMTP_EMAIL', "").split('@')[1] if os.getenv('SMTP_EMAIL') else None
+
     # Create the email message
     message = MIMEMultipart("alternative")
+    message['Message-ID'] = make_msgid(domain=sender_domain)
     message["From"] = email.utils.formataddr(
         (os.getenv('SMTP_SENDER_NAME', 'Room Booking'),
          os.getenv('SMTP_EMAIL')))