Miscellaneous topics that do not fit into specific categories.
That message means the recipient’s mail provider, for example Gmail in the message you shared, did not accept the email. It does not necessarily mean your Outlook account is broken.
First, please check your Sent Items folder. If you recognize the 27 emails, try sending again to one recipient at a time, remove large attachments, links, or signatures. If the same recipient keeps rejecting the email, they may need to add you as a safe sender or check with their email provider/admin, because Microsoft cannot force another provider’s server to accept a message.
If you do not recognize those 27 sent emails, please secure your Microsoft account immediately: change your password, review your recent sign-in activity, check for unknown forwarding or inbox rules, and enable two-step verification. Bounce messages for mail you did not send can indicate that someone accessed your account.