Hi John,
Thanks for clarifying that you’re using Outlook on the web (Outlook.com) the steps I shared earlier were for the desktop app so let’s adjust for the web version. In Outlook.com there is no Outbox folder like in the desktop app. Emails that fail to send usually remain in Drafts or they disappear if the send attempt was interrupted. Try checking your Drafts and Sent Items again to see if the message is there. You can also use the search bar at the top of Outlook.com by typing part of the subject or text from the missing email and selecting All folders in the search options. It’s also worth checking the Deleted Items folder because sometimes failed messages end up there automatically. If the email isn’t in any of these folders Outlook.com does not keep an Outbox for unsent messages so the message may have been lost during the failed send attempt in that case you’ll need to recreate the email.
Best regards,
Marcelo