The mail page under System tries SMTP, PHP mail() and both sendmail modes one by one or all at once, and saves the chosen way to .env without ever showing the password. IONOS answers everything under /.well-known/ itself with 403, so the address and HTTPS checks never reached the installation; the probe now lives at /kantsites-origin (ADR 122). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>