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)