Form submissions marked as not sent gave no reason: the transport exception was swallowed. Every send now goes through MailCheck, which logs the server's answer and a hint in German to var/log/mail.log (server lines only, no credentials). The system screen shows the mail route, sends a test mail to any address and lists recent attempts (ADR 121). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>