Thunderbird manual config validates hostname shape, not reachability

In Thunderbird account setup, the manual incoming/outgoing pages only validate that the hostname is syntactically well-formed. The wizard advancing from the incoming page to the outgoing page is therefore not evidence that the incoming settings are correct or that the server was ever contacted. When autoconfig fails it prefills both pages with a bare dotted domain that fails its own validator, and it prefills SMTP port 465, which Exchange Online rejects for client submission since it requires 587 with STARTTLS. Change the port and the connection-security dropdown together; setting one alone fails the connection test.