Fix Outlook SMTP server typo

From
https://support.microsoft.com/en-us/office/pop-imap-and-smtp-settings-for-outlook-com-d088b986-291d-42b8-9564-9c414e2aa040

README.md

@@ -385,7 +385,7 @@ You can also manually edit your own configuration, from scratch:
   backend.auth.raw = "*****"
 
   message.send.backend.type = "smtp"
-  message.send.backend.host = "smtp.mail.outlook.com"
+  message.send.backend.host = "smtp-mail.outlook.com"
   message.send.backend.port = 587
   message.send.backend.encryption = "start-tls"
   message.send.backend.login = "[email protected]"