Add message-id needed for finf-mails

pterClasses.py

+import hashlib
 import os
 import smtplib
 from dataclasses import dataclass
@@ -50,6 +51,7 @@ def sendFRMail(text: str, subject: str, sender: MailParticipant, receivers: List
     if ldapPassword is None:
         raise ValueError("Require ldapPassword")
     mail = MIMEMultipart()
+    mail['Message-Id'] = f"{hashlib.sha256(text.encode('utf-8')).hexdigest()}@pter.finf.uni-hannover.de"
     mail['Content-transfer-encoding'] = '8bit'
     mail['From'] = sender.alias
     mail['Subject'] = subject