Thunderbird asks <domain>/.well-known/autoconfig, Outlook POSTs to <domain>/Autodiscover, and both fell into portal's catch-all, which answers 200 with an HTML page - so a client got markup where it expected XML and went back to guessing. Both prefixes now go to Stalwart, which already generates the answers, templated on the address asked about. No static copy to drift out of date and no hostname of their own to certify. Host is rewritten to the name Stalwart has always answered for, and all three spellings of /Autodiscover are matched because Outlook is not consistent about it. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015GeH3y8fwTaTudaD88P57o