Adds X-Permitted-Cross-Domain-Policies (already highlighted in emphasize_stuff_in_headers() but never reported), Origin-Agent-Cluster, Document-Policy, Clear-Site-Data, Reporting-Endpoints, Report-To and NEL to run_security_headers(), all presence-only/INFO, matching how COOP/COEP/CORP were added in #2619.
When a port was appended to the domain (e.g. "--mx example.com:25"), the suffix was passed straight into the MX DNS lookup, so no MX records were found. Strip a trailing :port off the domain before the lookup and use it as the port to test. Also fix the no-MX message, which printed $1 (the run date) instead of the domain, plus a "records(s)" typo.
potato-20