add notes on tests with microsoft outlook.

summary: i haven't been able to send email.

compatibility.txt

@@ -1,3 +1,5 @@
 Known compatibility issues.
 
 - Autodiscovery with Microsoft Outlook (on macOS): Outlook appears to use a Microsoft service to fetch the configuration, instead of connecting directly. Their service makes an invalid TLS handshake (an SNI name with a trailing dot), which is rejected by the Go crypto/tls library. (2023-01)
+- Microsoft Outlook on macOS cannot sent messages. IMAP appears to work. During setup, an SMTP connection comes in, and AUTH PLAIN is successful. But the "Send" button is grayed out, so sending is not possible. There is probably something in our SMTP session that Outlook does not like. Though their logging only contains lines explaining SMTP was successful, both for SIZE and AUTH, with no mention of errors.
+- When adding an account in Microsoft Outlook on macOS with the "sync to microsoft cloud" checkbox checked (the default), you'll get incoming IMAP/SMTP connections from the cloud instead of from Outlook. IMAP works. SMTP for submission does not work. I'm seeing what appears to be a "LOGIN" SASL mechanism. A draft https://www.ietf.org/archive/id/draft-murchison-sasl-login-00.txt expired in 2004, and was created only to document that LOGIN is deprecated/obsolete. We don't announce support for LOGIN, because we don't support it. On top of that, they are sending SASL "initial client data", which is not allowed with the LOGIN mechanism. Perhaps our SMTP protocol responses have something weird to them that trigger this.