Issue #67: add the mode-switch postscript (#1081) and its troubleshooting row
Issue #67: app-only email sending — full write-up New page explaining why app-only mailboxes could not send, in plain English: what /me and /users/... actually mean, why the distinction only bites app-only, the two further faults behind the reported one, the fix, and why the implementation differs from the patch proposed in the issue. Mailbox-Authentication gains a developer section on the three things auth_mode changes, three troubleshooting rows, and a link to the new page. Sidebar updated.