This issue can occur when you register a 3rd party email address (e.g., an email address that is not or ) for your Microsoft Account and don't use for sending and receiving email. Recipients will also receive the email from the sender with the outlook_[long series of letters and recipients reply to the email, the email bounces and you may receive the message “Undeliverable message when you send Internet mail in Outlook.” Your email account name shows up as outlook_[long series of letters and the Folder Pane and when composing emails using Outlook for Windows. LessĪfter adding an email account to Outlook for Windows (Outlook 2016, 2013, 2010 versions) you may experience the following:
