app.config['MAIL_SERVER'] = 'smtp.ionos.co.uk' app.config['MAIL_PORT'] = 465 # change from 587 app.config['MAIL_USE_SSL'] = True app.config['MAIL_USE_TLS'] = False IONOS supports all three ports: 587 → TLS (STARTTLS) 465 → SSL 25 → fallback SMTP Step 4: Check Firewall/Antivirus Make sure your Windows Firewall or antivirus isn't blocking Python or the port you're trying to use. You can temporarily disable your firewall and test the reset again. Step 5: Use an App Password (if needed)