A new phishing attack has recently been discovered that pretends to be an Office 365 non-delivery message in order to steal your credentials.
While the email looks pretty legit, there are ways to prevent falling for these phishing attacks. The first and foremost indication is the “Send Again” box. Microsoft never gives an option to send emails again after they have failed. You will have to go back to your Outlook and send them manually. Secondly, failure messages arrive almost instantly after you send an email. Last but not least, always check for the link in the address bar and make sure it’s secured and is the official website.
Via: Bleeping Computer