Hello, I am currently facing difficulties with the automatic configuration of the Thunderbird mail client. I have set up a web server that provides an XML file containing the configuration information, accordingly to what we can see here -> https://wiki.mozilla.org/Thunderbird:Autoconfiguration:ConfigFileFormat, and the URL of the file is accessible without any problem from my host. However, when I try to configure Thunderbird to automatically retrieve the configuration, it doesn't seem to send an HTTP request to the server. I used wireshark to see what happens here and I can see a DNS request for autoconfig.mydomain and a response with the correct IP, but no HTTP request after that. I used the log console of thunderbird and I get those messages : mail.setup: guessConfig failed: Impossible de trouver un serveur Here's what I have checked so far: The configuration XML file has been validated and does not contain any syntax errors. The URL of the XML file is correct and accessible from a web browser. No proxy settings on my system. No firewall rules seems to be blocking my system to access autoconfig. Despite all these checks, I still can't resolve the issue. If you have encountered a similar problem or have any ideas about what might be causing this behavior, I would greatly appreciate it if you could share them. Here are some additional details that might be helpful: Operating System: Windows 11 Thunderbird Version: 115.0.1 (also tested on 102.5.1) The configuration XML file is accessible at this URL: http://autoconfig.<mydomain.com>/mail/config-v1.1.xml?emailaddress=<username>@<mydomain.com> Error message in the Thunderbird error console: "mail.setup: guessConfig failed: can't find a server" Thank you in advance for your help !